Case Studies: Fixture Design Solved

January 1, 2007
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Automotive suppliers are on the ball and have developed into an important economic factor. Numerous companies, including Weidmann Plastics Technology AG (Rapperswil, Switzerland), manufacture interior parts for well-known vehicle manufacturers.



Economical fixtures comprising of grid plate with screw jacks in use is shown on the measuring machine. Source: Witte LP


Automotive suppliers are on the ball and have developed into an important economic factor. Numerous companies, including Weidmann Plastics Technology AG (Rapperswil, Switzerland), manufacture interior parts for well-known vehicle manufacturers.
 
Weidmann specializes in manufacturing die-cast parts, though their manufacturing spectrum ranges from passenger-car battery covers to showerheads. Before new parts go into series manufacturing, they are dimensionally checked in the measurement engineering department.
Until recently, measurement predominantly took place in 2-D; today, demands are substantially higher and extensive 3-D measuring often is required. In order to measure plastic parts in a defined position, special fixtures are necessary.



A 3-D model of plastic parts is fixed on an Alufix Classic grid.
Source: Witte LP

In the past, fixtures were provided by a tooling department, and waiting longer than a week for the fixtures was not unusual. In order to avoid delays, and at the same time relieve the busy tooling department, Weidmann decided to change to a modular fixturing system. Weidmann’s measurement engineering department build their own individual fixtures independently when needed.

Peter Gilgen, 3-D measuring specialist, has been working with the modular system Alufix from Witte LP (Tucker, GA), for five years. “Once you understand the system, assembly is very easy,” he explains. “Setup is only limited to availability of our Alufix components. Because we work more and more with Alufix, we want to increase our range of items. The good thing is that the basic principle of the system never changes. That means any new parts always fit on our eight-year-old components.”

An advantage of the Alufix system is that the components are reusable. Because all fixtures are documented, it is not a problem to dismantle and later rebuild a fixture accurately. Thus, the existing Alufix material is not tied up for long periods of time and can be used for other jobs.



A plastic part is fixed on an Alufix Classic grid, 25 millimeters.
Source: Witte LP

The measurement engineering team works using two different measuring concepts. “On the one hand we have individual fixtures dedicated to a specific part,” says Gilgen. “On the other hand, we have complex fixtures that have to be preset on a measuring machine. Adjustment takes place on particular points specified by the customer. It is important that the fixtures are set up in such a way that they offer optimal access to measuring points and that the work piece is securely held. Mostly we are measuring free-form surfaces, in accuracy ranges of six-to-seven one-hundredths.”  

Mathias Schoppe, manager responsible for measuring at Weidmann Plastics Technology, says, “Plastic parts require special treatment. The material is often soft and the parts are unstable; distortion is the main problem. That means in order to gather accurate part data, the workpieces must not be clamped but only held in position. No pressure may be exerted on parts otherwise temporary deformation would result in incorrect measuring data.”

In order to optimize fixture building further, Weidmann started using Expert Design Software. Alufix Expert is a PC program for automatic fixture building on screen. It enables fast and simple implementation of complex fixture projects, allowing operators to simulate different types of supports on screen.

Part data supplied by the customer is entered into the software. According to the data entered, different types of setup are shown and can be changed on screen, allowing the operator to simulate the best possible configuration for the job.



The Alufix fixture without workpiece is shown here.
Source: Witte LP

Subsequently, fixture design takes previously defined support points into account. Beforehand, a list of Alufix components from the customer is entered into the software so that during design only existing elements available are incorporated.

For example, one project for the BMW Group was made up of 12 different work pieces. If each of these fixtures had gone to the tooling department to be manufactured, it would have meant considerably more organizational and economical expenditure to complete the entire project. The possibility of building fixtures using Alufix Expert speeded up actual fixture setup. In contrast to “on the spot” fixture building, which can involve a lot of trial and error, it was only necessary to set up according to the design.

Weidmann says using Expert makes it considerably easier to design a fixture according to the measuring points requested by a customer.

Part measuring is usually just prior to the start of series manufacture, at the time when design changes are sometimes made. The Alufix modular fixturing system gives operators the flexibility to change fixtures accordingly.

Witte LP
(770) 934-5449
www.wittelp.com
Reply 12



Sidebar: Benefits

  • The basic principle of the Alufix system never changes. New parts fit on old components.
  •  A substantial advantage of the system is that the components are reusable. Because all fixtures are documented, it is not a problem to dismantle and later rebuild a fixture accurately.
  • The Alufix modular fixturing system gives operators the flexibility to change fixtures accordingly.

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