CAD CAM Setup - CNC Information | Learn CNC

CAD CAM Setup

Include setup as part of CAD/CAM - computer-aided design; computer-aided manufacturing

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.

In this case, with the machine table display on the computer screen, Mr. Eastin opens a window on the screen and redraws the part as a separate CAD file. To simplify mounting the bracket on the fixture, Mr. Eastin draws three tabs on the workpiece. These tabs will be used to clamp the workpieces. After the workpiece is machined, the tabs will be removed at another station.

The windowing feature of the system lets him draft the workpieces in CAD while keeping the table display on the screen. When finished, he simply merges the two files--the workpiece drawing and the machining center table display. At this point, he can manipulate the workpieces on the machining center table to arrange them in the most efficient manner for machining. Now, with the workpieces positioned on the table, the fixture can be detailed.

Each machining center table in the CAS library is displayed two-dimensionally, complete with T-slot locations. Also illustrated, inside the table perimeter, is a smaller rectangle that represents the live area or usable work zone of the machine tool. Anything outside this live area is out of the spindle's reach for machining. Seeing this graphically helps assure the workpieces are correctly positioned within the machine's cutting range. Otherwise, the machine could over-travel trying to cut outside its live area and necessitate re-fixturing the workpiece before proceeding. CAS allows confirmation of this positioning information off-line, at the computer.

With the workpieces positioned on the table, Mr. Eastin draws a box around them with the computer mouse, creating the fixture subplate. The CAS software automatically dimensions this plate so the exact size material can be ordered or cut from stock.

Catalogs In A Computer

Detailing the subplate is simple with CAS. Resident in the library is the entire Carr Lane (St. Louis, Missouri) catalog of clamps, fixtures, and component parts. Selecting a clamp, holder, bolts or other hardware from the library requires simply entering the catalog part number into the computer. A family of parts is displayed on the screen and, with the mouse, Mr. Eastin picks out the components he needs. His selections are transferred graphically to the subplate drawing where he positions them, again using the mouse. A hard copy of this library transaction can be generated and used by the stockroom for processing, or serve as a bill of materials for an outside vender to fill. A quick check of the inventory determines what is available from stock and what needs to be ordered.

Dimensions for the workpiece program and fixture feature locations are taken from the machine tool home position (X-O, Y-O) which is shown on the CAS-generated table illustration. The setup drawing, NC program and machine tool all use the same reference point.

Putting It In A Program

Creating a program to machine the fixture is the next step in the process. To help the programmer, the Aura system shows both a top view and side view of the fixture with the workpieces in place. Seeing these relative positions helps identify potential tool path interferences so they can be avoided before the program goes to the shop floor. And seeing the setup arrangement lets a safety buffer be programmed into the tool's path.

First, Mr. Eastin programs the fixture. A library of machine speeds and feeds is resident in the CAM software. The programmer defines type of material and selects the tools and the speeds and feeds are automatically calculated. These speeds and feeds can be modified.

Essentially, once the tools are selected and the material specified, all that is left is assigning bolt hole locations for the two part blanks, spotting the locating pins for the second side and specifying the subplate hold-down bolt holes. All of the holes are co-bored except the part hold-down holes, which get tapped.

The workpiece gets programmed next. He generates the NC program using the merged CAD and CAS files, which let him see the workpiece, subplate, and fixture clamps all mounted on the machine table. The program for the first side calls for end milling the workpiece perimeter in two passes, milling five asymmetrical pockets, and milling three flats. For the second side, the workpiece is turned over and positioned against the locating pins. With the exception of milling the perimeter, the second side machining sequence is the mirror of the first.

Both programs are next downloaded to the machining center CNC. Since the machine home position is used to locate the subplate, no fixture offsets are needed the first time the job runs.

On The Shop Floor

The off-line work is complete. Part blanks are ready. The machine is tooled. Clamps are in-house. The subplate is on the machine. It's time to machine the fixture and workpieces--less than a day from the initial CAD input.

The machining of the subplate is straightforward. A spot drill starts the cycle by locating the subplate hold-down bolt holes, workpiece holding and locating pin holes, and setting ball hole. The tapped holes for the workpiece, pins and setting ball get pilot drilled. A half-inch drill prepares the holes for the subplate bolts. Next, a quarter-twenty tap finishes up the workpiece, locator pin and setting ball holes. The drill work is complete with a co-bore of the half-inch holes.

An end mill cleans up the back side of the subplate with a skim cut creating a surface to simplify alignment with the machine's X-axis the next time the plate is used. On subsequent setups, Mr. Eastin only needs to square the subplate with the machine's X-axis, establish an X-Y location using the setting ball, and enter a G-55 offset between the ball and the machine home position and he is ready to run the brackets again.

In about half an hour, the fixture is machined complete. The workpieces are machined alternately (as detailed above), side one workpiece one, turn it over and locate it against the pins for side two, load a blank workpiece for side one, and so on until the order is complete.

Is It For You?

Automating the production process to include machine setup has helped Ejay's compete and succeed. Many of the benefits Ejay's enjoys from its CAD/CAM system are transferable to most job shop operations:

* increased throughput of work

* shortened leadtimes from order entry to shipment

* reduced in-process inventory

* better documentation of each job

* improved spindle utilization

By improving his operation, Mr. Eastin is better able to serve his customers. In the competitive environment that job shops must operate, how fast you can hold a part may determine how long you can hold an order.

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