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Desk-top computer chassis moulded in DMC
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news
paiael-mounted Orbit Controls' T I P 900 programmable logic controller;, an X-axis dc motor controller (Fenner SpeedRanger); a Y-axis air-motor control module (Volstatic MAC222); A to B mould change-over relays; plus manual controls to ease positioning of spray gun carriages during initial set-up procedure. The control console is connected to the control system of a large 50 tonne hydraulic press, which allows one mould to be sprayed (mould A) whilst a second mould (mould B) is positioned under the press ram. When both the mould spray cycle and press cycle are completed, the press bed is shuttled across and mould B is sprayed while mould A is under the press. The spraying process consists of covering the mould to be sprayed with a dielectric hood, from which air is being extracted, and traversing up to 8 electrostatic powder spray guns along the X-axis of the mould and two powder spray
guns along the Y-axis. The movement of the spray hood into position and traversing of the powder spray guns are all controlled using proximity switches on the press and spray unit, which are connected to the TIP 90'0 programmable logic controller. Once the spraying cycle is complete, the PLC signals the press to raise the spray unit from the now-coated mould, move the press bed into position under the ram and initiate the pressing cycle. Whilst the pressing cycle is running, the operator may initiate spraying on the second mould. This is done by pushing a single push button, which simultaneously switches all input and output functions (proximity switches, X-axis motor and Y-axis motor) to the second side of the press and also starts the PLC. The second mould is now sprayed and the cycle repeated.
Computer housings switch to solid ABS
grade, Cycolac KJW, which is a fire retardant grade, replaces PPO (Noryl) foam. Savings will come from the ease of processing and the elimination of finishing steps. Apple has found that solid ABS processes in one third the time of PPO foam, which in long ,runs, enables the number of duplicate tools to be reduced by 40%. The PPO foam had to de-gas after moulding and then had to be filled, sanded and painted.
Designers at Apple, the American computer manufacturer, have switched to solid ABS from structural foam for the housing of the IIe personal computer. The Borg Warner
Desk-top computer chassis moulded in DMC The complex modular chassis (illustrated) for a new Burroughs desk-top minicomputer is moulded in DMC (BMC). Weighing 2.35 kg and measuring 350 x 350 x 165mm, the moulding is a complicated network of apertures and cutouts to accommodate sub-assemblies. Apart from having to position both mechanical and electronic components, the chassis provides a secure fixing for external cover panels using only four plastic fasteners. A maximum tolerance of 0.25mm is allowed on the larger dimensions. Also, the amount of open space in the chassis means that weld lines can pose a serious threat to the structural integrity and careful gating of the tool is essential. The chassis is transfer moulded on a 500 tonne Daniels press using vacuum to ensure complete filling of the cavity. Four cores, independently heated, are sequenced on alternate sides. The idea of using hydraulically operated side movers, an unusual technique on a compression tool, enables variations in the chassis design to be introduced more easily at a later date. Eleven ejectors ensure stress-free removal of the moulding. Actual moulding cycle time is approximately 4 minutes. A grade of BIP's Beetle D M C was selected which had very low shrinkage and easy flow characteristics, as well as UL94 V-0 approval at the relevant section thicknesses. From preparation of a mock-up chassis from machined DMC (BIV[C) shapes, to supply of the first sample mouldings is said to have taken 18 weeks, full-scale production of mouldings now being underway.
MATERIALS & DESIGN, Vol, 4 OCTOBER/NOVEMBER 1983
851
news
paiael-mounted Orbit Controls' T I P 900 programmable logic controller;, an X-axis dc motor controller (Fenner SpeedRanger); a Y-axis air-motor control module (Volstatic MAC222); A to B mould change-over relays; plus manual controls to ease positioning of spray gun carriages during initial set-up procedure. The control console is connected to the control system of a large 50 tonne hydraulic press, which allows one mould to be sprayed (mould A) whilst a second mould (mould B) is positioned under the press ram. When both the mould spray cycle and press cycle are completed, the press bed is shuttled across and mould B is sprayed while mould A is under the press. The spraying process consists of covering the mould to be sprayed with a dielectric hood, from which air is being extracted, and traversing up to 8 electrostatic powder spray guns along the X-axis of the mould and two powder spray
guns along the Y-axis. The movement of the spray hood into position and traversing of the powder spray guns are all controlled using proximity switches on the press and spray unit, which are connected to the TIP 90'0 programmable logic controller. Once the spraying cycle is complete, the PLC signals the press to raise the spray unit from the now-coated mould, move the press bed into position under the ram and initiate the pressing cycle. Whilst the pressing cycle is running, the operator may initiate spraying on the second mould. This is done by pushing a single push button, which simultaneously switches all input and output functions (proximity switches, X-axis motor and Y-axis motor) to the second side of the press and also starts the PLC. The second mould is now sprayed and the cycle repeated.
Computer housings switch to solid ABS
grade, Cycolac KJW, which is a fire retardant grade, replaces PPO (Noryl) foam. Savings will come from the ease of processing and the elimination of finishing steps. Apple has found that solid ABS processes in one third the time of PPO foam, which in long ,runs, enables the number of duplicate tools to be reduced by 40%. The PPO foam had to de-gas after moulding and then had to be filled, sanded and painted.
Designers at Apple, the American computer manufacturer, have switched to solid ABS from structural foam for the housing of the IIe personal computer. The Borg Warner
Desk-top computer chassis moulded in DMC The complex modular chassis (illustrated) for a new Burroughs desk-top minicomputer is moulded in DMC (BMC). Weighing 2.35 kg and measuring 350 x 350 x 165mm, the moulding is a complicated network of apertures and cutouts to accommodate sub-assemblies. Apart from having to position both mechanical and electronic components, the chassis provides a secure fixing for external cover panels using only four plastic fasteners. A maximum tolerance of 0.25mm is allowed on the larger dimensions. Also, the amount of open space in the chassis means that weld lines can pose a serious threat to the structural integrity and careful gating of the tool is essential. The chassis is transfer moulded on a 500 tonne Daniels press using vacuum to ensure complete filling of the cavity. Four cores, independently heated, are sequenced on alternate sides. The idea of using hydraulically operated side movers, an unusual technique on a compression tool, enables variations in the chassis design to be introduced more easily at a later date. Eleven ejectors ensure stress-free removal of the moulding. Actual moulding cycle time is approximately 4 minutes. A grade of BIP's Beetle D M C was selected which had very low shrinkage and easy flow characteristics, as well as UL94 V-0 approval at the relevant section thicknesses. From preparation of a mock-up chassis from machined DMC (BIV[C) shapes, to supply of the first sample mouldings is said to have taken 18 weeks, full-scale production of mouldings now being underway.
MATERIALS & DESIGN, Vol, 4 OCTOBER/NOVEMBER 1983
851