GB2463019A

GB2463019A - Method of clamping a cast body during machining and a cast body therefor

Info

Publication number: GB2463019A
Application number: GB0815599A
Authority: GB
Inventors: Gilles Bordenet
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2008-08-28
Filing date: 2008-08-28
Publication date: 2010-03-03
Also published as: GB0815599D0

Abstract

A method of machining opposite faces of a cast automatic transmission valve body by placing the body on locator pads and clamping thereon with no lateral offset between the locator pads and members which provide the clamping force. A first face of the body is then machined, the body is then turned over, again clamped with no lateral offset and then the face opposite the first face is machined. Also a cast body which is provided with a first area for clamping when machining a first face of the body and a second area for clamping when machining an opposite face.

Description

I

DESCRIPTION

Process for machining a casting piece The invention concerns a process for machining a casting piece in which the casting piece is machined on two opposite faces, the casting piece being put on locators pads and being machined on its first side in a first machining operation, the casting piece being then flipped over and being machined on its second face in a second machining operation. The invention concerns also a casting piece to be machined on two opposite faces.

Many casting pieces, for instance valve bodies for automatic transmissions, have to be machined on two opposite faces in order to achieve the desired surface qualtity and the requested dimensions.

The current machining process is as follows: the casting piece is put on three locators pads and then one channel face is machined. After this step, the piece is flipped over and rests on the channel face of the already machined surface. It is clamped on the pads of the over side and the rest of the machining is done.

However, after machining a face deflection can often be observed. The fact that the casting piece does not have flat surfaces after machining leads to problems at the next steps of the production process as well as to quality problems with the finished product.

The objective of the invention is therefore to improve the flatness of the casting piece and to avoid the above-mentioned face deflection.

This object is achieved according to the invention in that the casting piece is clamped during the first and the second machining operations without any lateral offset between the locators pads and the clamp area.

The following considerations have been made in order to overcome the described flatness problem. An analysis of the current machining process of casting pieces has shown that after flipping the piece over, there is a lateral offset between the locators pads and the clamp area which results during the machining operation in a bending moment deflecting the piece. The deflection may be quite important depending on the stiffness of the casting piece.

According to the invention, the deflection of the casting piece is avoided in that there is no offset between the locators pads and the clamp area, so that the clamping load is reacting directly on the surface which is being machined. This improves the flatness of the casting piece and also its dimensional precision in terms of parallelism, true position of bores and other features, circularity, cylindricity, etc. A casting piece to be machined on two opposite faces, wherein the casting piece is provided with a first clamp area for the locators pads during a first machining operation on the first face and a second clamp area for the locators pads during a second machining operation is also within the scope of the invention.

In order to be able to avoid the lateral offset during both of the machining operations, it is useful to provide two distinct clamp areas for the two machining operations so that during both machining operations there is a direct support of the casted piece under the clamp load.

In the following, the invention is described in detail with reference to the drawings in which FIGURE la to id show the first and second machining

operations according to the prior art, the

casting piece being respectively represented in front view and in right side view; FIGURE 2a to 2d show the first and second machining operations according to the invention, the casting piece being respectively represented in front view and in right side view.

The casting piece shown in these figures is a valve body for an automatic transmission.

As represented in FIGURES la to lb showing the first machining operation according to the prior art, the casting piece 1 is put on locators pads 2 datum A and is then machined on its first face. The machining comprises all bores, features and channel faces.

Then the casting piece 1 is flipped over and it rests on its already machined surface 3 (in the present case, the channel face) as shown in FIGURES ic and id. The casting piece 1 is clamped on the over side of the pads (the face to be machined during the second machining operation). The clamping force acting on the casting piece 1 is symbolized S. As shown in FIGURE ic and id, there is an offset between the locators pad 2 and the clamp force S so that a bending moment acts on the casting piece 1. This bending moment leads to a distortion of the casting piece 1 which may be rather important depending on the stiffness of the casting piece 1. Even for rather stiff parts, the flatness of the casting piece 1 suffers significantly leading to problems in the further fabrication steps or during use of the casting piece 1.

As represented in FIGURES 2a to 2b showing the first machining operation according to the invention, the casting piece 1 is put on a first set of locators pads 2 datum A and is then machined on its first face. The machining comprises all requested bores, features and channel faces.

Then the casting piece 1 is flipped over and it rests on its already machined surface 3 (in the present case, the channel face) as shown in FIGURES 2c and 2d. The casting piece 1 is clamped on the over side of the locators pads 2. The clamping load acting on the casting piece 1 is symbolized S. As shown in FIGURES 2c and 2d, there is no offset between the locators pads 2 and the clamp force S so that no bending moment acts on the casting piece 1. In this case, the clamping load is reacting directly over the locators pads 2 so that the flatness of the casting piece 1 does not suffer from the second machining operation.

Claims

CLAIMS1. A process for machining a casting piece in which the casting piece is machined on two opposite faces, the casting piece being put on locators pads and being machined on its first side in a first machining operation, the casting piece being then flipped over and being machined on its second face in a second machining operation, characterized in that the casting piece (1) is clamped during the first and the second machining operation without any lateral offset between the locators pads (2) and the clamp area.
2. A casting piece to be machined on two opposite faces, characterized in that the casting piece is provided with a first clamp area for the clamping during a first machining operation on the first face and a second clamp area for the clamping during a second machining operation.