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Software automates punch manufacture.

What seemed to be up-to-date technology got old fast. Ram-type electrical-discharge machines (EDMs) made an infinite number of finished die shapes and sizes from 80 different blank die sizes at Mate Punch and Die Company, Anoka, MN, and made them well. But operators got tired of graphite dust and aligning new electrodes. Engineers got tired of forcing the EDM units to maintain high accuracy. This modern technology seemed dirty, labor intensive, and not all that efficient.

The solution to the problem, of course, was wire EDM. But managers didn't stop there. They planned total untended automation from the top down, using CAD/CAM to the full letter of its promise.

Let's take another look at the "old" way. For more than ten years, Mate used a two-step process to cut the many different shapes of punches and dies for NC turret punch presses. First, operators roughed standardized soft blanks and then, after off-plant heat treatment, cut the final shape with ram EDMs using graphite electrodes.

The process had more problems than the dust from machining graphite electrodes. The inventory of roughed shapes became cumbersome; there was too much individual tool handling; and setup was burdensome, requiring time to recheck and reset electrodes to exactly the same orientation in which they were cut.

Robotic EDM is the core

After months of analysis, reports, and proposals, engineers set up a test cell using two Charmilles wire EDM machines serviced by an ASEA robot. These systems formed the core of the entire project, which now has ten wire EDM units, the robot, and a 52-ft track. The robot is supplied by ABB, New Berlin, WI, and the EDMs by Charmilles Technologies Corp, Mount Prospect, IL. After assembling the machines and support equipment, Mate contracted with Automated Control Systems of Minneapolis Inc, Minneapolis, MN, to integrate the system and write the software for the cell controller. The cell software controls all workpiece flow and is the central hub for all other machines and computers. It sorts and prioritizes customer orders, interprets CMM inspection results, makes appropriate offsets, prints identification chits, and also initiates error warnings.

The cell-control software ensures that the system follows the most efficient sequence for manufacturing-running the most critical parts first. The system operates completely untended and provides improved die quality and consistency. The robot automatically loads dies into collets to speed production, and untended overnight operation further improves efficiency and cuts cost.

After the order

Initially, tooling orders go into Mate's business computer, an NCR 10,000 Model 75. The computer then downloads product-order specifications to an Altos minicomputer and then through a PLC to the robot and the Charmilles wire-EDM machines. The system keeps track of parts movement through the inspection phase, and each EDM unit has its own input and output buffer station for holding in-process and completed parts.

Orders also go to the engineering department, which provides application advice, CAD/CAM processing to eliminate errors in manufacturing, and centerline drawings to accompany die sets for user machine programming and reordering. Orders for special punches and dies let engineers take advantage of the computer-aided-design (CAD) system. It doesn't take long to come up with a final design for special shapes, louvers, etc.

Once the final design enters the system, the robot and EDMs take over. However, to operate the cell in a completely untended mode, inspection is critical. It requires feedback capability to send data back to the cell controller to automatically adjust the EDM machines.

To handle this task, View Engineering, Madison Heights, MI, provided a turnkey vision-inspection system for the die cell. Based on a noncontact type coordinate measuring machine (CMM), it inspects all dies for size, concentricity, and angularity. It confirms part quality and, by uploading results to the cell controller, it allows the long untended EDM runs (see box).

Overall software

Such a complex system doesn't run without extensive programming. We talked with Brad Tutch, president of Automated Control Systems of Minneapolis, to learn more about the software. In addition to a broad overview, he had to consider such details as the need for an input parts buffer for View's CMM to hold the next part to be inspected, and an output buffer for the completed part. His programs had to account for 72 fixtures for 80 different part sizes, all stored in a modified 18-drawer cabinet, accessed by a robot. An additional 80 sizes of blank parts were stored in a rack manually loaded from outside the cell.

Brad Tutch told T&P that it started out simply enough. Mate asked him to integrate the View machine into the cell to automate production. He made the following notes:

* The cell controller must handle communication to the mainframe. He chose an IBM-compatible' 386 20 Mhz industrial PC.

* The software to run the cell was written in Turbo C language by Brad Tutch and Mate programmers, enabling an extremely fast control program.

* A menuing system keeps the operator interface as simple and intuitive as possible. The operator can monitor the entire system at a glance, or watch communications with the PLC, mainframe, or inspection machine. Cell-resource information (EDM fixtures, blanks, etc) and pending orders are also a keystroke away.

* The PLC that interfaces between the PC and the wire-EDM cell has many responsibilities. It must communicate with the robot, start the EDMs at the appropriate times, coordinate delivery of finished parts to shipping, open and close the mechanical fixture-buffer drawers (electronically queued), index blanks to proper position for the robot, and provide the PC with status of cell switches.

* The PC also has many jobs. First, it must download new orders, using an Altos computer and software to communicate between the cell-controller PLC and the individual CNC controls on the Charmilles EDMs. Then, it must instruct Altos to send a particular program to an EDM, resort all orders each time a new batch is received update system data on the computer screen, print a log of cell activity, print a chit to identify each part, and provide priority scheduling-mainly to keep the EDMs busy.

Staying on track

A well-written program keeps law and order in complex systems. Here, the scheduler handles the EDMs in numerical order. Some of the priority checks are as follows:

Highest. Remove finished part and reload next one; remove part in output parts buffer and bring to the CMM input buffer. If an EDM is empty and its input buffer is empty, load input buffer with the next part, and then load EDM fixture.

Load CMM with part from its input buffer, and initiate inspection procedure. Exchange incorrect fixtures. Load EDM fixture with part from input buffer. Process fixture removal from cell or addition to cell. Finally, remove part from View upon inspection and place it on the shipping conveyor (if passed), or in the scrap bin (if failed).

Lowest. Load EDM input buffer with next blank.

Orders for new parts are downloaded via an RS-232 port between the Altos and the cell computer. The cell computer initiates all requests for action, and the Altos is programmed to perform the following tasks:

* Transmit new orders (every 3 min, or by request).

* Send an order (its coordinate file) to an EDM.

* Delete an order upon inspection (if passed).

* Send coordinate offset information to an EDM.

* Reinitialize entire system.

* Transmit current Altos status.

Tidying up

The cell computer polls system I/O status every 0.25 sec, performing I/O updates on demand and at regular intervals. Updates initiate such tasks as robot operation, EDM start-up, blank-buffer-row cocking, and fixture-drawer commands.

Commands sent to the robot are handled by the PLC. There are 24 input and 24 output lines dedicated for this purpose. The sequence of events for the robot are:

1) Place the task number and the ID number of the destination on the Output bus.

2) After acknowledgement, place the task number and the part number on the output bus.

Handshaking is performed by using one I/O bit for each side to acknowledge receipt of the previous command.

The cell software, then, controls all part flow and allows the system to run untended. The systems house, Automated Control Systems, also designed and wired the PLC that is the central hub for all communication between the cell controller and all other machines and computers. The cell controller interprets inspection results and directs machine offsets continuously.

Other components

A successful untended system relies on teamwork from a lot of suppliers and vendors. For example, Positrol, Cincinnati, OH, designed and built the custom collets that hold the dies on center. The repeatable performance of these collets made robot loading possible. They improve quality because they hold each die around the entire OD while it's being machined.

Industrial Magnetics Inc, Boyne City, MI, designed the robot's end effector. IMI developed two prototype units before centering on a final design. The flat-bottom electromagnet picks up any die from the top with one end effector.

Alliance Engineering Inc, Maple Grove, MN, designed the conveyor, and Dimension Industries Inc, Maple Grove, MN, built it. Initially, engineers needed the conveyor to buffer finished parts. But then they straightened the conveyor's layout to transport dies to shipping. Paper is not needed, and there are no extra handling costs. Parts don't get marked or damaged, because no operator touches the die set until shipping.

Finally, Donaldson Company Inc, Minneapolis, MN, designed a central filtration system for the wire EDMs. It delivers pure water at a constant temperature, needed for consistent EDMing. Quality water helps ensure quality parts, and operators can change the filters with no machine downtime. Additional software was written to allow the Charmilles to communicate with the Altos. The software makes it possible to automatically download programs to the EDM units, reduces operator time, and cuts machine downtime for program downloading. It's vital to running untended, and it eliminates lost die sets, because all parts are made without paper to misplace.

The Charmilles EDM units are among the few that can request a program from the Altos computer, and they are consistent running, say Mate engineers. These are features necessary for untended operation, along with consistent self-threading capability and the ability to accept machine offsets from another computer to compensate for concentricity shifts over time.

Consistent is the key word for automation.

The robot and track provide consistent loading of dies into collets, which not only keeps the system working all night, but also improves workpiece quality. Does it really work? Since the system became operational, the accuracy of concentricity and angularity of Mate's Slug Free[R] dies is better than ever, according to Mate engineers. The wire EDM machines cut finished shapes from hardened blanks in one step without requiring a large inventory of roughed-out standard shapes. And, by running the system continuously, Mate gets a third more production or what amounts to a third shift without adding labor costs. The system is an example of CAD/CAM and computer control that really works.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

Article Details
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Title Annotation:production automation at Mate Punch and Die Company, includes related article on automated flexible inspection
Author:Miller, Paul C.
Publication:Tooling & Production
Article Type:Company Profile
Date:Aug 1, 1991
Previous Article:Information system: key to competitive edge.
Next Article:The quest for quality: sixth-inning scorecard.

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