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Intelligent Redesign Cuts Cost in Half

March 3, 1999

3 Min Read
Intelligent Redesign Cuts Cost in Half

When you push a key on a computer keyboard, a rubber or elastomeric mat under the keys flexes to transmit the signal, then returns the key to its start position. Traditionally, keyboard mats have been compression moulded of natural rubber. Starlim GmbH, a liquid injection moulding (LIM) moulder of liquid silicone rubber (LSR) in Marchtrenk, Austria, saw that as a challenge.

Liquid silicone rubber costs four times as much as rubber. Starlim could not change that. So they changed the part instead. The redesign (see photo) cut the finished part weight by more than half — from 65g to 30g — and significantly improved the mat's performance and durability. The new design also permitted Starlim to apply its unique, patented mould technology and automated, tiebarless injection systems. As a result of all this, the product, with improved performance, costs only half of what it did before.

Proprietary Mouldmaking Technology

The critical part of a keyboard mat is the "dome" under each key. It gives the right feel to the user, lets the signal be sent to the computer, and repositions the key. In effect, Starlim changed what had been a solid mat to a connected series of domes. Thomas Bründl, Starlim's managing director, said the company designed special equipment to measure the resistance of the domes by force wave diagrams. Each dome needs to withstand 30 million pushes with no performance change. Starlim's testing resulted in a second membrane being added to each dome for performance enhancement. That, plus the long-term resilience of LSR, Bayer Silopren in this case, raised performance far above previous specifications. The special equipment is now used for quality testing.

The new design's pattern of domes and thin connecting strips might seem to present a problem in positioning gates to assure proper filling, but Starlim was actually using one of its own strengths. The technology of Starlim's sister toolmaking company, Sterner GmbH, located in an adjoining building, allows placement of a nozzle under each dome: 109 domes, 109 nozzles, each with a cold runner, in an area the size of a computer keyboard.

Sterner's patented nozzle design has no valve, therefore the nozzle is constantly open. Temperature and pressure of the vulcanizing LSR, controlled by proprietary processing technology, seal off the material flow. The mould design completely eliminates flash, which in turn eliminates material waste and trimming time. Nozzle openings can be as small as 0.25 mm and they seal so cleanly that gate marks are hard to see. The absence of moving parts makes moulds easier to construct, longer lasting, and eliminates nozzle maintenance.

Tiebarless Moulding, Precise Controls

The mat is moulded in a 40-second cycle time (considerably faster than the previous compression cycle) on a robot-equipped, tiebarless 250-ton Engel injection system. The absence of tiebars allows the robot, an Engel ERC, to strip the mat horizontally from the mould, exit the mould horizontally, turn the mat, and place it on a belt that puts it in a shipping carton.

Thomas Bründl notes that the robot, since it doesn't need the vertical motion to avoid tiebars, costs less and has extra time to perform other functions. Starlim, which has just moved across the street to a new, two-level, 8,000- sq-m facility, has more than 30 Engel machines ranging from 20 to 250 tons. That number will soon grow to 60. All the new machines will be tiebarless, robot-equipped Engels with the control software modified to optimize Starlim's processing technology.

Starlim produces a wide variety of LSR parts and two-component parts using LSR for markets such as automotive, medical, electrical/electronics, pharmaceutical, baby care, and appliances. The company has designed its own LSR dosing system and material handling technology to cope with moulded parts such as 2-mm washers weighing less than 1g. ISO 9001 certification was received two years ago, and the company is nearing QS 9000 certification for the automotive industry.

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