Slide 1

The problem. The problem was that the router had a Dremel unit fitted, which was OK for small work, but to use a larger router tip, I would need a larger router to use 1/4inch and 1/8 shank tools. Slide 2 The problem. I tried fitting a die-grinder, but that was too noisy, so I purchased a hole saw from ALDI, but the snout was too short resulting in the tool being too high to the work piece. This called for a new bracket to position the tool closer Slide 3 The Pattern. A new bracket could have been fabricated, but not having the welding facility, I decided to go with a casting Slide 4 The solution. The result is very satisfactory. Slide 5 Pattern Design Or How to get a casting, the shape and price thats wanted. During our pursuit of our hobby, whether the power source be in clockwork, steam, electric or internal combustion, we will eventually need to produce a component that can be fabricated, or one which can be cast. It is my aim this evening to give you some pointers towards obtaining or producing a casting which is both the required shape, and for the best price. Slide 6 Manufacture of Metal Components by the casting process. Melt metal by heating. Pour molten metal into suitable container. Allow metal to cool and solidify. Separate solid component from container. Remove excess metal. Inspect component. Machine if required. May help with understanding the process. (Gradual build up) I would like to concentrate on the whys and how's leading to the production of a suitable container. Slide 7 Factors affecting choice of moulding method. Metal to be cast. Number of castings required. Casting tolerances. Complexity of casting design. Surface finish required. How accurate does the casting need to be? The more accurate, the more expensive. Slide 8 Summary of casting processes. Metal to be cast.Quantity of castings to be made. LowHigh Moulding process choice is determined firstly by the metal to be cast Slide 9 Summary of casting processes. Metal to be cast.Quantity of castings to be made. LowHigh Ferrous metals. (Iron & Steel) High Melting point. Non-ferrous metals. (Aluminium,Brass, Zinc alloys) And the number of castings required. Firstly the ferrous metals, iron, steels Slide 10 Summary of casting processes. Metal to be cast.Quantity of castings to be made. LowHigh Ferrous metals. (Iron & Steel) High Melting point. Sand Moulds Manually produced Sand moulds Automatically produced Non-ferrous metals. (Aluminium,Brass, Zinc alloys) These types of metals are usually poured into moulds made from sand which have a surface coating to prevent metal penetration. Small numbers of steel castings are made by hand using some form of chemical binder; while cast iron castings traditionally use greensand. Slide 11 Summary of casting processes. Metal to be cast.Quantity of castings to be made. LowHigh Ferrous metals. (Iron & Steel) High Melting point. Sand Moulds Manually produced Sand moulds Automatically produced Non-ferrous metals. (Aluminium,Brass, Zinc alloys) Sand moulds Manually produced Permanent moulds (Metal, rubber, carbon) Non-ferrous metals are again made using greensand, although it is becoming more common for a number of copper based alloys to use chemical binders. The low numbers are the processes which we would normally be involved with. So now lets refresh your memories on what greensand moulding involves Slide 12 Making a sand mould. Because of the file size of the film that was shown, this has not been included here but can be downloaded separately (Sand Mould.mpg). Slide 13 Pattern Materials Timber - master patterns, one-off & low numbers. Metal - large numbers. Plastics - multiple patterns, production. Polystyrene foam - one-off. Plaster. Composites low numbers. Patterns for this type of moulding can be made from any material which can withstand the punishment Slide 14 Pattern Allowances Contraction Machining Taper or Draft How accurate does the casting need to be? The more accurate, the more expensive. Slide 15 Solidification Solid Contraction Solidification Contraction Liquid contraction As molten metal cools, it passes through three phases of what is loosely termed contraction The first is while it is still liquid, which is called liquid contraction, and the next is the solidification stage, where alloys pass through a pasty or mushy phase. These first two phases are dealt with by the foundry, and the final solid contraction stage is dealt with by the patternmaker, who makes the pattern a little larger than the required casting. This allowance is dependant on the metal being cast. Slide 16 Cooling During the solidification of the casting, the heat energy that it contains is passed into the surrounding mould. A thin layer or skin is formed, which conforms to the mould cavity; which is followed by consecutive layers. Solid metal, like its liquid stage, occupies a smaller volume, and this, if not dealt with by the foundry, forms defective cavities inside the casting. Slide 17 Contraction Allowance Material CastRule AllowancePercentage Magnesium Steel1:352.857% Plane Carbon Steel1:502.000% Brass/Bronze1:701.428% Aluminium1:801.250% Grey Cast Iron1:1001.000% Nodular Iron1:1200.833% The bottom four metals are the ones which we most commonly encounter The most common method of solving the problem, was for the patternmaker to use a contraction rule. These came with addition readily allowed for in the rule itself. Today with the metric system, the patternmaker calculates the additional material to be added to the pattern. Slide 18 Machining Allowance Material Casting Size (mm) 0