Include setup as part of CAD/CAM

Modern Machine Shop, Oct, 1992 by Chris Koepfer

It makes sense to program within the context of the total setup--including machine and fixture--to save time in the shop.

Often, machine setup is analogous to "mop-up," those pre-production loose-ends, usually relegated to the shop floor for remedy. But, many of those loose ends can be handled off-line with a software package that integrates setup--machine selection, workpiece holding and fixture machining--with workpiece programming, taking much of the setup burden off the machinist.

Some of the setup chores like finding clamps, getting stock, locating T-bolts, dialing in the fixture and more still must be performed on the shop floor. However, many of the decisions such as what size stock, how long the T-bolts need to be, what size clamp and where to position the fixture relative to machine zero, can be done off-line.

Computer-aided setup (CAS), does for setup what the other C-acronyms do for design and manufacturing, moving many time-consuming setup adjustments off-line. The goal of CAS, like computer-aided design (CAD) and computer-aided manufacturing (CAM), is to keep the machine tool cutting. Tying up a machine tool for extensive setup is a poor use of a valuable resource.

The output of most CAD/CAM systems is a workpiece print and an NC program. The print is a picture of the workpiece with its mathematical description. The NC file is a program that instructs the machine how, with what tool, and in what order the workpiece should be processed.

But output from the CAD/CAM system only gets the process started. Everything else is left for completion on the shop floor, such as:

* what is the actual work zone of the table

* where hold-down clamps locate

* what size and type of clamps are needed

* interference zones

* a program for machining a subplate, when needed

* a plan for holding the workpiece

* how to locate the part

* location of work zero point

These setup questions can be readily answered, off-line, using CAS. In some cases, setup time reductions of 75 percent have been reported. And with such significant savings possible using CAS software, setup is being reconsidered for inclusion as an integral part of workpiece programming.

Why CAS?

The idea behind CAS is to incorporate setup into planning the machining of a workpiece--from the start. It works hand-in-glove with CAD and CAM to answer most setup questions off-line, before they are asked on the shop floor. But how is it done? Sky Eastin has an answer that he uses in his job shop.

Mr. Eastin operates Ejay's Machine Company Inc., a 26-year-old, family owned job shop located in Fullerton, California. The company is known for producing high-quality, geometrically complicated parts, generally in small quantities. Although they occasionally work with ferrous materials and titanium, aluminum is used for most jobs. Much of the credit for Ejay's success goes to Mr. Eastin's common-sense manufacturing approach and proficiency as a machinist but he is aided by a CAD/CAM system configured to consider setup in the workpiece programming process.

Mr. Eastin bought into CAS about four years ago with a system from Aura CAD/CAM Inc. (El Segundo, California). It runs on an Apple Macintosh computer and features fully integrated CAD, CAM and CAS functionality. No translator is needed between the databases. Mr. Eastin can draw a workpiece in CAD, create a program to machine it in CAM and configure the workholding fixture in CAS, all during one sitting at his PC. Because the system is integrated, work from one area, CAD for example, can be directly accessed for programming in CAM--it is all part of the same system. And bundled into the system is setup software (CAS) that can give the shop floor the additional benefit of a picture of the setup that shows how to hold the workpiece.

Testimony to Ejay's success as an aerospace supplier is a pair of framed documents hung in the front lobby. One, from Boeing, attests to Ejay's inclusion in the D1-9000 total quality program. A second plaque is from the company's major customer, McDonnell Douglas. It identifies Ejay's as one of a very select number of companies to receive DAC-SQS certification from McDonnell Douglas.

Pick A Table

To illustrate how the CAD/CAM/CAS system works, Mr. Eastin takes us through the steps he uses to manufacture a landing gear bracket for the McDonnell Douglas C-17 aircraft. The workpiece is an L-shaped bracket made from aluminum and the production run is nine pieces. The bracket blank is created from aluminum sheet stock, rough cut on a band saw.

The first process decision is which machine will run the bracket. The decision is aided by calling up schematics of the shop's machining center work-tables, resident in the system database. This library contains worktable configurations for the shop's machining centers. In the case of the bracket, since two can be machined in one setup on the shop's 20-inch by 40-inch Amura vertical machining center, it is the machine of choice for this job.

Initial input for the bracket, like many of Ejay's jobs, is a blueprint. Other parts may arrive in the form of floppy disks, or scaled vellums that can be digitized. Whatever format the input uses, with the exception of floppy disk inputs, the workpiece is redrawn in CAD.