CN103212914A - External sound field type titanium-alloy manual welding device and welding method - Google Patents
External sound field type titanium-alloy manual welding device and welding method Download PDFInfo
- Publication number
- CN103212914A CN103212914A CN2013101726938A CN201310172693A CN103212914A CN 103212914 A CN103212914 A CN 103212914A CN 2013101726938 A CN2013101726938 A CN 2013101726938A CN 201310172693 A CN201310172693 A CN 201310172693A CN 103212914 A CN103212914 A CN 103212914A
- Authority
- CN
- China
- Prior art keywords
- welding
- ultrasonic
- tig
- arc
- switch
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Landscapes
- Arc Welding In General (AREA)
- Arc Welding Control (AREA)
Abstract
The invention discloses an external sound field type titanium-alloy manual welding device which is characterized in that an ultrasonic vibration body consisting of an ultrasonic transducer and an ultrasonic amplitude transformer is sleeved on a ceramic nozzle at the front part of a TIG (tungsten inert gas) welding torch through a central hole, and the TIG welding torch, the ultrasonic transducer and the ultrasonic amplitude transformer are in a coaxial line so as to increase the radiation area. The welding torch is provided with a welding switch, an ultrasonic switch and a fine-tuning mechanism, and the opening and closing of an air relay in an ultrasonic generator can be controlled through triggering the ultrasonic switch, thereby eliminating the high-frequency interference in the process of TIG arc-striking. A welding method comprises the following steps of: firstly enabling a tungsten electrode of the welding torch to be coincident with the axes of the ultrasonic transducer and the ultrasonic amplitude transformer; starting a TIG welding machine, triggering a button of the welding switch, and carrying out arc-striking according to a conventional TIG welding method; and handholding and operating the welding torch, adjusting the angles of the welding torch and a workpiece, and implementing an operation of welding according to the welding position, thereby realizing the ultrasonic TIG compound welding of titanium alloys. The device and method disclosed by the invention are strong in adaptability, not limited by the sizes of workpieces, suitable for all-position welding, and strong in practicability, and have a good improvement effect on the attachment joints of titanium alloys and other materials.
Description
Technical field
The invention belongs to the arc welding technical field of titanium alloy, the sound field formula that adds titanium alloy manual welding device and welding method that specifically equipment is simple, easy to operate.
Background technology
As everyone knows, titanium alloy is as a kind of lightweight, high-strength, corrosion resistant alloy material, use in a lot of fields in Aero-Space and people's daily life, and use more and more widely, in the application of a lot of structural members, will certainly run between titanium alloy or the connectivity problem of titanium alloy and other storeroom, at present, the method of attachment that relates to has diffusion welding (DW), friction welding (FW), explosive welding (EW), TIG weldering, Laser Welding, electron beam welding, soldering etc., and its not enough complicated operation connects weak effect.
The vibration that ultrasonic vibration produces can make the whole upwards translation of TIG static characteristic of arc, and arc length La and spoke side height H are mated when good, and arc voltage raises obvious under the ultrasonication.Arc length and spoke side height are 2-26,3-24,4-24,5-20(unit: in the time of mm), move the amplitude maximum on the static characteristic of arc curve on year-on-year basis; When ultrasonic vibration acted on the TIG welding arc, electric arc can produce to the center compression effects, and electric arc conduction cross-sectional area reduces; By the law of resistance as can be known, dwindled the sectional area of current lead-through, whole external resistance has been increased, its electric potential gradient also will increase, and electric current shows as arc voltage when constant and raises the arc energy increase.And along with electric arc is compressed, arc center's district's particle density increases, in the electron motion process, also just increase with cation or argon gas atmo collision probability, and then the mean free path of shortening free electron, show as on the macroscopic view under the constant prerequisite of welding current, need bigger arc voltage to increase the directed translational speed of conducting particles, because the free path that collision brings reduces, show as the increase of welding seam deep width ratio under the arcing to overcome.
Summary of the invention
The objective of the invention is to overcome the deficiencies in the prior art, a kind of mode by mechanical couplings is provided, the sound field formula that adds titanium alloy manual welding device and welding method that hand-held general T IG welding gun and ultrasonic vibration system are coupled and form.
The present invention can reach by following measure.
A kind of sound field formula titanium alloy manual welding device that adds, comprise hand-held TIG welding gun, ultrasonic transducer and ultrasonic amplitude transformer are formed ultrasonic vibrator, it is characterized in that the ultrasonic vibrator that ultrasonic transducer and ultrasonic amplitude transformer are formed is set in TIG welding gun leading section ceramic nozzle place through centre bore, the TIG welding gun, ultrasonic transducer and ultrasonic amplitude transformer coaxial line, generally contract in ultrasonic amplitude transformer in TIG welding gun end, the luffing boom end is the stage shape, to increase swept area. the welding switch is installed on the welding gun, ultrasonic switch and micro-adjusting mechanism, can control the switching of air relay in the supersonic generator, the High-frequency Interference when getting rid of the TIG starting the arc by triggering ultrasonic switch.
A kind of sound field formula titanium alloy welding method that adds is characterized in that step is as follows:
Step 1: at first regulate hand-held TIG welding gun tungsten electrode and ultrasonic transducer and ultrasonic amplitude transformer dead in line, regulate the relative position of ultrasonic vibrator and TIG welding gun by turn fine-tuning nut knob, measure and regulate the size of luffing bar stage surface of emission height H and TIG welding gun tungsten electrode and workpiece distance L a, make when welding ultrasonic field the effect of electric arc is reached the strongest, the corresponding relation of spoke side height and arc length is: first group of H=20mm, La=5mm, second group of H=24mm, La=3 ~ 4mm, the 3rd group of H=26mm, La=2mm;
Step 2: start tig arc welding machine, trigger the welding shift knob, the TIG welding method starting the arc routinely, trigger the ultrasonic switch button after the starting the arc, air relay closes in the supersonic generator, connect supersonic generator, 50Hz power frequency electricity is converted to 15kHz ~ 100kHz high-frequency electrical, through ultrasonic vibration installation high-frequency electrical is converted into the same frequency mechanical oscillation that amplitude is 10-150 μ m again;
Step 3: the hand-held welding gun, adjust welding gun and workpiece angle, weld according to the welding position, realize the ultrasonic TIG composite welding of titanium alloy;
Step 4: trigger the ultrasonic switch button once more, the air relay disconnects, and ultrasonic vibration stops; Trigger the welding switch, welding arc extinguishes, and guarantees the time 0 ~ 30s that supplies gas that lags behind, treat the cooling of titanium alloy test specimen after, remove welding gun, finish welding process.
High strength supersonic of the present invention is when liquid state is propagated, can in metal bath, produce the acoustic streaming effect, acoustic streaming is to destroying the boundary layer, quicken mass-and heat-transfer, smashing the nascent thick β phase crystal grain of titanium alloy, improve heterogeneous nucleation rate, promote the subparticle disperse to play the effect of crystal grain thinning, the arc pressure that acts on the welding pool improves, and welding penetration significantly increases, and has improved welding efficiency greatly; After while adding in welding process is ultrasonic, crystallite dimension in overheated zone and heat affected area part reduces, improve joint fatigue strength and plasticity, and Technological adaptability of the present invention is strong, not limited by workpiece size, be fit to all-position welding, practical, all have good improvement effect to titanium alloy self or with the jointing of other material.
Description of drawings
Fig. 1 is the experiment device schematic diagram of the inventive method.
Fig. 2 is that the present invention specifically welds schematic diagram.
Mark among the figure: tungsten electrode 1, vernier knob 2, ultrasonic switch 3, welding switch 4, welding gun 5, ultrasonic transducer 6, ultrasonic variable amplitude bar 7.
The specific embodiment
Below in conjunction with accompanying drawing the present invention is further described.
As shown in the figure, a kind of sound field formula titanium alloy manual welding device that adds, comprise hand-held TIG welding gun 5, ultrasonic transducer 6 and ultrasonic amplitude transformer 7 are formed ultrasonic vibrator, it is characterized in that the ultrasonic vibrator that ultrasonic transducer 6 and ultrasonic amplitude transformer 7 are formed is set in TIG welding gun 5 leading section ceramic nozzle places through centre bore, TIG welding gun 5, ultrasonic transducer 6 and ultrasonic amplitude transformer 7 coaxial lines, contract in ultrasonic amplitude transformer 7 in TIG welding gun 5 ends, luffing bar 7 ends are the stage shape, to increase swept area. welding switch 4 is installed on the welding gun 5, ultrasonic switch 3 and micro-adjusting mechanism 2, can control the switching of air relay in the supersonic generator, the High-frequency Interference when getting rid of the TIG starting the arc by triggering ultrasonic switch 3.
A kind of sound field formula titanium alloy welding method that adds is characterized in that step is as follows:
Step 1: the tungsten electrode 1 and ultrasonic transmitter dead in line of at first regulating hand-held TIG welding gun 5, regulate the relative position of the rifle body of ultrasonic vibrator and TIG welding gun 5 by turn fine-tuning nut 2 knobs, measure and regulate the size of luffing bar stage surface of emission height H and TIG welding gun tungsten electrode and workpiece distance L a, make when welding ultrasonic field the effect of electric arc is reached the strongest, the corresponding relation of spoke side height and arc length is: first group of H=20mm, La=5mm, second group of H=24mm, La=3 ~ 4mm, the 3rd group of H=26mm, La=2mm;
Step 2: start tig arc welding machine, trigger welding shift knob 4, the TIG welding method starting the arc routinely, trigger the ultrasonic switch button after the starting the arc, air relay closes in the supersonic generator, connect supersonic generator, 50Hz power frequency electricity is converted to 15kHz ~ 100kHz high-frequency electrical, through ultrasonic vibration installation high-frequency electrical is converted into the same frequency mechanical oscillation that amplitude is 10-150 μ m again;
Step 3: hand-held welding gun 5, adjust welding gun and workpiece angle, weld according to the welding position, realize the ultrasonic TIG composite welding of titanium alloy;
Step 4: trigger ultrasonic switch 3 buttons once more, the air relay disconnects, and ultrasonic vibration stops; Trigger the welding switch, welding arc extinguishes, and guarantees the time 0 ~ 30s that supplies gas that lags behind, treat the cooling of titanium alloy test specimen after, remove welding gun, finish welding process.
High strength supersonic of the present invention is when liquid state is propagated, can in metal bath, produce the acoustic streaming effect, acoustic streaming is to destroying the boundary layer, quicken mass-and heat-transfer, smashing the nascent thick β phase crystal grain of titanium alloy, improve heterogeneous nucleation rate, promote the subparticle disperse to play the effect of crystal grain thinning, the arc pressure that acts on the welding pool improves, and welding penetration significantly increases, and has improved welding efficiency greatly; After while adding in welding process is ultrasonic, crystallite dimension in overheated zone and heat affected area part reduces, improve joint fatigue strength and plasticity, and Technological adaptability of the present invention is strong, not limited by workpiece size, be fit to all-position welding, practical, all have good improvement effect to titanium alloy self or with the jointing of other material.
The mode of the present invention by mechanical couplings is coupled in hand-held general T IG welding gun rifle body in the ultrasonic vibration installation through hole of being made up of ultrasonic transducer and ultrasonic amplitude transformer and guarantees that both are coaxial, luffing bar and ultrasonic transducer reach resonance, ultrasonic-frequency power supply is produced, frequency is converted into the same frequency mechanical oscillation of ultrasonic amplitude transformer emitting facet at the continuously adjustable supersonic frequency alternate electrical signal of 15kHz ~ 100kHz, titanium alloy T IG arc-welding method welds routinely, the switching of air relay in the ultrasonic switch control supersonic generator, to get rid of the mutual interference mutually of ultrasonic-frequency power supply and TIG starting the arc high-frequency signal, arc-plasma is subjected to the effect of arc space ultrasonic field, improve arc plasma concentration of energy degree, change electric arc below melt flows and crystallization behavior, strengthen weld penetration and improve welding seam tissue capability.
Titanium alloy because of have excellent mechanical properties such as high strength, good corrosion resistance, high-heat strength, density are little be widely used in aerospace industry in making the important structure material and the low pressure depressor machine dish and the blade of aero-engine, thereby replace stainless steel, heat resisting steel as the structural metal.At present, the most frequently used method of titanium alloy welding is the TIG weldering, do not concentrate yet the TIG welding has, and arc energy density is low, welding arc distributes, cause efficient low, when adopting big standard, because titanium alloy fusing point height, thermal capacity is big, thermal conductivity factor is little often causes that the weld zone is overheated, weld grain is organized thick, and the joint plasticity and toughness are not enough and the welding deformation increase.Influence joint mechanical property and structural entity life-span.
The objective of the invention is to propose a kind of sound field formula titanium alloy manual welding method that adds, the manual welding gun rifle of general T IG body is coupled in the inner assurance of the ultrasonic vibration system mesopore of being made up of coaxial ultrasonic transducer and luffing bar, and both are coaxial, two trigger switches are installed on the welding gun, can control the closure of air relay in the supersonic generator by triggering ultrasonic switch, use with the opening to reach, get rid of the purpose of High-frequency Interference.During welding, apply the high density ultrasonic energy on the welding arc simultaneously, under the situation of identical heat input, because the ultrasonic field effect makes arc energy more concentrated, the arc pressure that acts on the welding pool improves, and welding penetration significantly increases, and has improved welding efficiency greatly; In welding process, add simultaneously ultrasonic after, reduce in the crystallite dimension of overheated zone and heat affected area part, improve joint fatigue strength and plasticity.And Technological adaptability of the present invention is strong, not limited by workpiece size, is fit to all-position welding, and is practical, all has good improvement effect to titanium alloy self or with the jointing of other material.
Claims (2)
1. one kind adds sound field formula titanium alloy manual welding device, comprise hand-held TIG welding gun, ultrasonic transducer and ultrasonic amplitude transformer are formed ultrasonic vibrator, it is characterized in that the ultrasonic vibrator that ultrasonic transducer and ultrasonic amplitude transformer are formed is set in TIG welding gun leading section ceramic nozzle place through centre bore, the TIG welding gun, ultrasonic transducer and ultrasonic amplitude transformer coaxial line, increase swept area. the welding switch is installed on the welding gun, ultrasonic switch and micro-adjusting mechanism, can control the switching of air relay in the supersonic generator, the High-frequency Interference when getting rid of the TIG starting the arc by triggering ultrasonic switch.
2. one kind adds sound field formula titanium alloy welding method, it is characterized in that step is as follows:
Step 1: at first regulate hand-held TIG welding gun tungsten electrode and ultrasonic transducer and ultrasonic amplitude transformer dead in line, regulate the relative position of ultrasonic vibrator and TIG welding gun by turn fine-tuning nut knob, measure and regulate the size of luffing bar stage surface of emission height H and TIG welding gun tungsten electrode and workpiece distance L a, make when welding ultrasonic field the effect of electric arc is reached the strongest, the corresponding relation of spoke side height and arc length is: first group of H=20mm, La=5mm, second group of H=24mm, La=3 ~ 4mm, the 3rd group of H=26mm, La=2mm;
Step 2: start tig arc welding machine, trigger the welding shift knob, the TIG welding method starting the arc routinely, trigger the ultrasonic switch button after the starting the arc, air relay closes in the supersonic generator, connect supersonic generator, 50Hz power frequency electricity is converted to 15kHz ~ 100kHz high-frequency electrical, through ultrasonic vibration installation high-frequency electrical is converted into the same frequency mechanical oscillation that amplitude is 10-150 μ m again;
Step 3: the hand-held welding gun, adjust welding gun and workpiece angle, weld according to the welding position, realize the ultrasonic TIG composite welding of titanium alloy;
Step 4: trigger the ultrasonic switch button once more, the air relay disconnects, and ultrasonic vibration stops; Trigger the welding switch, welding arc extinguishes, and guarantees the time 0 ~ 30s that supplies gas that lags behind, treat the cooling of titanium alloy test specimen after, remove welding gun, finish welding process.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310172693.8A CN103212914B (en) | 2013-05-13 | 2013-05-13 | A kind of additional sound field formula titanium alloy Manual welding device and welding method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201310172693.8A CN103212914B (en) | 2013-05-13 | 2013-05-13 | A kind of additional sound field formula titanium alloy Manual welding device and welding method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN103212914A true CN103212914A (en) | 2013-07-24 |
| CN103212914B CN103212914B (en) | 2016-04-06 |
Family
ID=48811246
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201310172693.8A Active CN103212914B (en) | 2013-05-13 | 2013-05-13 | A kind of additional sound field formula titanium alloy Manual welding device and welding method |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN103212914B (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104526174A (en) * | 2014-12-15 | 2015-04-22 | 赵辉 | Ultrasonic plasma arc welding process and device |
| CN104588893A (en) * | 2014-12-15 | 2015-05-06 | 赵辉 | Plasma arc ultrasonic welding process and device |
| RU188681U1 (en) * | 2018-12-29 | 2019-04-22 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) | Device for non-consumable electrode welding using ultrasonic vibrations |
| CN110977216A (en) * | 2019-12-20 | 2020-04-10 | 哈尔滨工业大学 | Novel pulse ultrasonic electric arc composite welding device and welding method thereof |
| RU2817683C1 (en) * | 2023-09-27 | 2024-04-18 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) | Non-consumable electrode welding method of aluminium and its alloys |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2826512A1 (en) * | 1978-06-16 | 1980-01-03 | Siemens Ag | Combined ultrasonic and electric resistance welding appts. - for welding metals coated with oxide |
| CN1583340A (en) * | 2004-06-03 | 2005-02-23 | 清华大学 | Titanium alloy welding method based on arc ultrasonic process |
| CN101219499A (en) * | 2007-11-23 | 2008-07-16 | 哈尔滨工业大学 | Composite welding method of ultrasound wave and non-melt pole electrical arc |
| CN101947696A (en) * | 2010-09-26 | 2011-01-19 | 哈尔滨工业大学 | Welding device for compounding ultrasonic focusing sound field with molten pole arc welding |
| CN102581498A (en) * | 2012-02-25 | 2012-07-18 | 哈尔滨工业大学（威海） | Welding device for combining ultrasonic focusing sound field with non-melt pole by electric arc welding |
-
2013
- 2013-05-13 CN CN201310172693.8A patent/CN103212914B/en active Active
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2826512A1 (en) * | 1978-06-16 | 1980-01-03 | Siemens Ag | Combined ultrasonic and electric resistance welding appts. - for welding metals coated with oxide |
| CN1583340A (en) * | 2004-06-03 | 2005-02-23 | 清华大学 | Titanium alloy welding method based on arc ultrasonic process |
| CN101219499A (en) * | 2007-11-23 | 2008-07-16 | 哈尔滨工业大学 | Composite welding method of ultrasound wave and non-melt pole electrical arc |
| CN101947696A (en) * | 2010-09-26 | 2011-01-19 | 哈尔滨工业大学 | Welding device for compounding ultrasonic focusing sound field with molten pole arc welding |
| CN102581498A (en) * | 2012-02-25 | 2012-07-18 | 哈尔滨工业大学（威海） | Welding device for combining ultrasonic focusing sound field with non-melt pole by electric arc welding |
Non-Patent Citations (2)
| Title |
|---|
| 孙清洁: "超声-TIG电弧复合焊接方法及电弧行为研究", 《中国博士学位论文全文数据库 工程科技Ⅰ辑 》, no. 4, 15 April 2011 (2011-04-15), pages 51 - 53 * |
| 王帅: "铝合金超声-TIG焊接工艺及超声作用效果研究", 《中国优秀硕士学位论文全文数据库 工程科技I辑》, no. 5, 15 May 2011 (2011-05-15), pages 14 - 15 * |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104526174A (en) * | 2014-12-15 | 2015-04-22 | 赵辉 | Ultrasonic plasma arc welding process and device |
| CN104588893A (en) * | 2014-12-15 | 2015-05-06 | 赵辉 | Plasma arc ultrasonic welding process and device |
| RU188681U1 (en) * | 2018-12-29 | 2019-04-22 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) | Device for non-consumable electrode welding using ultrasonic vibrations |
| CN110977216A (en) * | 2019-12-20 | 2020-04-10 | 哈尔滨工业大学 | Novel pulse ultrasonic electric arc composite welding device and welding method thereof |
| RU2817683C1 (en) * | 2023-09-27 | 2024-04-18 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Волгоградский государственный технический университет" (ВолгГТУ) | Non-consumable electrode welding method of aluminium and its alloys |
Also Published As
| Publication number | Publication date |
|---|---|
| CN103212914B (en) | 2016-04-06 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Wu et al. | Review on magnetically controlled arc welding process | |
| Sun et al. | Penetration increase of AISI 304 using ultrasonic assisted tungsten inert gas welding | |
| da Cunha et al. | Ultrasound in arc welding: A review | |
| CN109365965B (en) | Welding molten drop transition control equipment and control method based on superaudio pulse double-tungsten electrode coordination | |
| CN100577340C (en) | Composite welding method of ultrasound wave and non-melt pole electrical arc | |
| WO2018145543A1 (en) | Dual heat source hybrid welding torch and welding method | |
| CN101947696A (en) | Welding device for compounding ultrasonic focusing sound field with molten pole arc welding | |
| CN109604831B (en) | Laser TIG (tungsten inert gas) hybrid welding process for improving laser welding undercut of titanium and titanium alloy sheets | |
| CN108857112B (en) | Two-dimensional ultrasonic vibration auxiliary melting welding device and method | |
| JP2003504213A (en) | Composite laser and plasma arc machining torch and method | |
| CN103785963B (en) | A kind of ultrasonic electric arc composite welding apparatus | |
| CN103143848B (en) | Vertical welding method for applying ultrasonic-arc hybrid | |
| CN103212914B (en) | A kind of additional sound field formula titanium alloy Manual welding device and welding method | |
| CN104741805B (en) | A kind of Aluminium Alloy with Pulsed ultrasonic electric arc composite welding apparatus and welding method thereof | |
| CN105562894A (en) | Device applying pulsed TIG electric arc for assisting MIG welding and welding method achieved by adopting device | |
| Fan et al. | Arc character and droplet transfer of pulsed ultrasonic wave-assisted GMAW | |
| WO2018145544A1 (en) | Welding torch used for laser beam-plasma arc hybrid welding | |
| CN105195875B (en) | Lockhole effect TIG deep penetration welding welding guns | |
| CN105215552A (en) | A kind of stainless steel welding | |
| US11161191B2 (en) | Process and apparatus for welding workpiece having heat sensitive material | |
| Zhang et al. | Effect of pulse frequency on weld appearance of Al alloy in pulse power ultrasonic assisted GMAW | |
| CN105234539B (en) | The plasma arc welding (PAW) connection device and technique of a kind of ultrasonic wave added perforation | |
| CN206455302U (en) | It is a kind of to be used for laser beam and the welding torch of plasma arc composite welding | |
| CN105618933B (en) | A kind of efficiently high-quality laser micro arc plasma complex welding method | |
| CN112846458A (en) | Ultra-low heat input welding device and welding method for metal sheet |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant |