Robots cut gaskets and costs.

Extruded and formed auto door gaskets - known in auto manufacturing as "glass runs" - are actually quite complex parts. Design must take into account the chemistry and physical properties of the rubber; the profile of the cross section; and contained metal reinforcing. In addition, glass contacting surfaces need an even coating of a fibrous floc to allow a smooth slide of glass over the run.

Several forms of support metal are used: solid metal profiles; lanced and formed light gage metal; and Schlegal Wire, which is formed and woven with string. Figure 1a shows a length and cross-section of a typical auto door gasket. Once an extruded gasket form is produced, the second of the challenge emerges - cutting and shaping gaskets into auto door glass runs.

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Length cuts involve the support metal as well as the rubber. All cuts must be precise so that later forming and molded corners will fit the contours of the door frame. Required sealing and appearance qualities must be maintained. Figure 1b is a photo of cut pieces; then an assembled completed door glass run.

Machine configuration and control

A completely new approach in producing glass runs was used for the 2001 Ford Explorers. New robotic cells were designed, built and used in daily production operations. The automated robot systems are built by Computer Age Engineering (CAE). CAE has built a variety of automated production equipment and has many years of experience in providing machines for rubber manufacturers.

Each machine is basically a customized robotic cell wherein the robot tooling consists of a circular saw and a hot knife (figure 2). The robot is enclosed within a standard protective cell with the "front" cell wall being a two-sided workpiece holding fixture. The workpiece fixture is sequentially pivoted to present rough-cut gasket lengths to the robot for programmed precise cutting and notching operations.

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Robot cutter 2

The robot is a six-axis ABB IRB 4400 capable of handling up to 132 lbs. with rapid movement. The seven-inch saw blade cuts at a rate of a half-meter per second and the blade is water mist cooled and lubricated. For this particular application, the robot control system acts as a simple I/O device in a production cell controlled by an Allen-Bradley SLC/500 PLC.

An operator unloads and loads the "outside" workpiece fixture while the robot is making a programmed sequence of cuts on the inside fixture. The operator controls the indexing. When the fixture is in place and locked, the PLC provides a signal enabling the robot to proceed with the saw cutting sequence. The hot knife is programmed to make tapering "skive" cuts for finished fits with the door metal.

The two workholding fixtures are nearly mirror images of each other and the robot is programmed to alternately produce left side and right side glass runs. In this manner, two fixture swings produce a complete auto set which is convenient for follow-on packaging and shipping. Figure 3 is a photo of a workholding fixture which accommodates all pieces required for one side of a vehicle.

Both sides of the workholding fixture also include pneumatic powered die cutters which perform required notching while the fixture is locked in place for the robot cuts. The notches allow neat fits around various fasteners and door hardware.

Along with the robot and indexing fixture station, the robot cutter cell system includes a comprehensive cell safety system plus an operator work station with a vivid flat screen display and touch screen controls. The safety system is typical of robot cells and has sensing mats within the cell which prevent operation with anyone inside the enclosure.

Operational features and performance

The ABB Model IRB 4400 robot was originally designed for foundry operations and, along with its 132 lbs. wrist-handling power, features better seals and mechanism protection. This model allows the robot to be simultaneously tooled with a saw blade and hot knife which can then be indexed as required. The temperature of the hot knife, can be closely controlled over a wide range of several hundred degrees.

For a four door vehicle, each door's glass run is comprised of front and rear pillar pieces along with top headers. For the new Ford Explorers, five pieces are precision cut to form a glass run set for one side of the vehicle. These five pieces require over thirty cuts to form the angular ends precisely cut flaps for assembling and molding into a finished glass run.

Robot cutter 3

A major requirement in finished glass runs is a neat skive cut which uses the hot knife to make tapering cuts so that the run provides a smooth, sealing interface with the door metal forming the window openings. Skive cuts made by the robot cutter cell have been of exceptionally high quality.

In production test runs, cycle times are averaging about one minute per cut sequence. Or, a complete car set of glass runs can be produced every two minutes.

Estimates to produce the required quantities using prior equipment and methods involved nine different machines and 27 production persons. The robot cutter system will use four identical machines and will require 12 production people. The initial capital costs for the robot cutter cells are in the order of 10% to 15% higher than the nine-machine total. However, with the labor savings alone, users can expect the investment differential to pay back within the first few weeks of production.

Built-in flexibility

The prior production method used dedicated cutting units for each glass run piece and a total balanced output hinged on all machines being up and running. Each robot cutter cell produces complete car sets so that a cell being down is simply a proportionate drop in production rate (which ostensibly could be made up in weekend work).

Further, the life of the prior tooling was usually only a few years or until significant vehicle configuration changes were made. In contrast, the robot cutter cell fixtures are easily retrofitted and the robot re-programmed to handle a wide range of similar products. Thus, it appears that the robotic cells will have a much longer production life.

Also, occasional needs to reactivate old tooling for aftermarket orders were previously labor-intensive efforts. The robot cutter cells can handle such tasks by a simple fixture change plus re-loading saved programs.

Ken Ball is an engineering physicist with over 30 years of experience with industrial instrument and control systems. He has designed and installed control systems for industrial plants and missile facilities.