Clamping filigree parts

Transcription

1 Clamping filigree parts August 2005 Getting a good hold on bits and pieces For almost all shapes and sizes of parts there are suitable clamping technologies available on the market. However demands on clamping systems increase when parts are very large or very small. Conventional methods often cannot ensure acceptable results. When we are talking about non-magnetizeable parts with complicated shapes the following clamping methods provide good solutions depending on requirements: 1. Vacuum clamping technology 2. Freeze technology 3. Moulding technology 4. Modular clamping systems for measuring 1. Vacuum clamping technology This method, originally predestined for milling work on parts with large surfaces, meanwhile also provides solutions for any kinds of shapes and materials. For really small parts special fixtures usually have to be designed and manufactured. Vacuum chuck for bottle tops Photo 1: Plastic bottle tops clamped on custom built chuck. This type of chuck has been manufactured several times for different shapes and sizes of parts. Vacuum ensures fast, multiple, even, distortion-free clamping of these parts, which are otherwise difficult to position and hold accurately and repeatably for measuring. 1

2 Clamping new wafers When extremely fragile parts have to be positioned, equipment with a gentle surface is required. Witte Bleckede, specialists in manufacturing custom built clamping systems, use porous material which securely but gently fixes flat parts into position. Deformation is ruled out as sensitive parts are clamped over whole surface on porous insert without any holes or slots which could affect thin materials like foils. One advantage compared with conventional vacuum clamping is that free areas on the chuck can remain uncovered. Chucks can be used for workpieces with different dimensions without requiring any adaptation. Tried and tested clamping technology and custom built vacuum chucks with Metapor inserts are in high demand in semiconductor and micro-electronic industries. Processing wafers requires special handling. Disks, usually round and only a few 100µm thick, on which electronic devices like integrated circuits are manufactured using different technical processes, are mostly made of silicon. In microsystem technology glass wafer disks with 1mm thickness are also used. Wafers are manufactured in different diameters/dimensions, the larger they are the more circuits are involved. Extreme demands are made with regard to evenness of wafer, perfection of polish and cleanness of surface. Only unevenness of a few nm (millionths of a millimetre) over the whole surface is acceptable. This means high requirements on clamping systems have to be met. Photo 2: Vacuum chuck for wafer blanks Chuck with eight individual clamping areas for holding silicon wafers. Each area can be switched on and off independently. The square shape leads us to suppose that wafer blanks will be processed. In this phase clamping is possible using vacuum grid. Holes outside clamping areas are for mounting locating pins and stops. Plate accuracy is 0,02mm/100mm 2

3 Photo, Photo 3a: Metapor chucks for measuring wafers: This chuck is used in quality control. It comprises of a basic unit and exchangeable adapter plates for checking wafers with different diameters. Clamping area is an insert of porous Metapor. Plate shown above has 2 clamping areas which are operated individually according to need. This unit is equipped with a temperature gauge when used on measuring machine. Photo 4: Extremely accurate Metapor vacuum chucks with top and bottom surfaces machined. Five clamping areas on these chucks enable measuring of 5 different sized wafers. Tolerances are 0,005mm (5 µm). 3

4 Photo 5: Sinter chucks for use on lapping machine Lapping machines are used to achieve finishing of part surfaces, removing as little material as possible whilst maintaining tight tolerances. For this process parts, usually hard materials like steel or ceramic are vacuum clamped onto these chucks with sinter metal inserts. Photo 6: Custom built chuck for lathe This Metapor chuck is used on a lathe for holding copper circuit boards of a cell-phone key panel. The cutting tool moves from the centre outwards resulting in a circular pattern on the panel. Metapor made an ideal clamping surface for machining parts with thickness of 0,2mm down to 0,17mm. Not having to cover unused areas was an added advantage in this application. 4

5 2. Freeze technology with Ice Vice Witte offers different systems for clamping with ice. An Ice-Vice Light version with 40x40mm clamping area has been specially developed for really small parts. Clamping them for machining jobs presents a particularly difficult problem, even more so when they have complicated geometries. Ice-Vice can solve a lot of those problems. Contact points of parts freeze securely and evenly on a film of water in seconds. Holding force is distributed evenly over the whole surface Ice-Vice is often used in model, sample and prototype building as well as for single item manufacturing. Photo 7: Ice-Vice Light for small parts Part freeze-clamped on to 40x40mm area in seconds using a drop of water. Photo 8: Typical Ice-Vice candidates Small electronic parts pre-destined for clamping on Ice-Vice 5

6 In practice After unit has been cooled down to +3C, spray a little water onto clamping area and position part; freezing takes place at -10 C. The speed of this process depends on warmth conductivity, warmth retaining property and size of part as well as temperature in surrounding environment. Pre-cooling, freezing and thawing are operated by switches on the surface. Ice Vice Light is very compact (223 x 67 x 84mm) and is an economical alternative for special small series manufacture. Both above methods require a certain amount of flat area for clamping. The next method describes clamping spherical parts. 3. Mould clamp technology with Weiguss Spherically complicated and at the same time delicate prototype, design or small series parts are fixed securely quickly and economically for machining. Mould clamp technology allows tension free positioning of different shaped parts. Photo 9: In practice Clamp raw material using vacuum and mill first side without milling through completely, locate part using pins on the vacuum chuck. Fill up milled out cavities with Weiguss alloy which has been melted to a fluid state, resulting in a flat surface. After cooling down part is turned over and again clamped with vacuum. Machining on reverse side is now a simple process. 6

7 To release part simply put in a water bath at around 79 C to melt reusable Weiguss then it is ready to use again and again, and again. Photo 10, Photo 10a: Typical Weiguss candidates - left: mirror holders, right: fluid aligners. Square cutouts have been made using a cylindrical tool with Dia. 0,3mm. 130 of these were clamped and machined in one process from a blank measuring 200x300mm. Layout was made by CAD/CAM/CNC. Locating pins enabled accurate positioning after turning whole thing around when machining on first side was finished. 3D spherically complicated concave as well as convex contours are possible with this method, all parts only need to be moved twice. 4. Modular fixturing technology for dimensional checking Clamping with modular elements For holding different parts which constantly change in shape and size Alufix Modular Fixturing System from Witte is an ideal solution. It puts users in a position to build individual fixtures quickly on the spot. The material can be reused again and again. For those really small parts Witte offers mini modular elements in aluminium and acryl in XS size, which are most suited for measuring applications. 7

8 Photo 11: Clamping small plastic parts using modular elements Picture shows a switch element with outer dimensions 20x20mm mounted on an AF XS Acryl fixture. Set up leaves slots, protrusions and position of holder free for measuring in one clamping process. These kind of fixtures are well suited for series measuring due to their excellent repeatable accuracy. For more efficient operation up to 20 parts are mounted to one plate and checked quickly one after the other. Photo 12 : Tiny part held with AF XS Very small plastic joint held in AF XS Acryl for customer in medical technology. The user s problem was how to hold this 2,5mm part for measuring. Diameter of tip is 0,5mm. 8