Machining the Die Cavities
As will be noticed from [Fig. 30], the machinery in the die-making department is of modern design, for no other class of work demands as good tool equipment and as much skill in the making as die-casting molds. The die-blocks are made of machinery steel. [Fig. 34] illustrates the first step in making a die-casting mold after the die-block has been shaped approximately to size. This operation consists in carefully facing off the die surfaces on a vertical-spindle grinding machine. This, of course, is a quick method of surfacing the die-block, and it insures that the top and bottom surfaces of these plates will be parallel, permitting the die-faces to come together properly.
Fig. 33. Section through a Die-casting Mold
The next step consists of laying out the die, as shown in [Fig. 36]. This is done in the usual manner, by working on a coppered surface, using dividers, scales, and a center punch. When laying out the die, the necessary allowances are made for shrinkage and finish, these points having been planned before actual work on the die has been started. As in other phases of die-work, the machining operations are performed, as far as possible, before any hand-work is done. In [Fig. 38] may be seen a die-maker turning the cavity in a part of the die-casting mold. The highest type of skilled workmanship is called for on this machine work, and as may be surmised from [Fig. 38], where the die-maker is shown measuring the die with a vernier caliper, the measurements must be exact, for no grinding operations follow the machine work.
Fig. 34. First step in making the Mold—Grinding Surfaces of Blocks
Fig. 35. A Milling Operation on a Die
[Figs. 35] and [39] show typical milling operations being performed on die-casting molds. In [Fig. 39] the diemaker is shown indicating a pin in one corner of the mold cavity, preparatory to doing additional milling. The block is held in the usual manner by being clamped on the bed of the milling machine, and after it has been properly located under the cutter head, tools are substituted for the indicator and the milling of the cavity is completed. [Fig. 35] shows one of the sections of the die-casting mold which is to be used in producing the casting shown at the right of the work. In this case the diemaker is milling the recess for the steel arbor which may be seen directly in the foreground. This will be fitted in place to provide for the forming of the hole in the side of the piece.
Fig. 36. Laying out One of the Mold Parts
Fig. 37. Planning the Die-casting Mold
Fig. 38. Turning out a Die-casting Mold
Fig. 39. Indicating a Mold on the Milling Machine
[Fig. 40] illustrates several important points in the making of a die-casting mold. This illustration shows the ejector box with the lower half of the mold on it, the ejector plate being held against the under side of the die-plate by means of the pinion shaft. The operation being done is the drilling of the ejector-pin holes. Referring back to [Fig. 32], which by the way shows the die here illustrated disassembled, the holes being drilled are those shown at F for the reception of the pins E. The method employed is to drill the holes through the die and into the ejector plate, afterward reaming all holes to size and driving the pins into position in the ejector plate, while they are allowed to slide freely through the die-plate. We will now assume that the ejector box and plate have been completed and fitted, a pinion shaft for operating this plate also fitted, the lower and upper dies completed by the machining operations previously described, and all assembled. The final operation of the fitting of the pins is shown in [Fig. 41] in which the die-maker may be seen filing off the ends of these pins so that when dropped to the lower position they will lie flush with the surface. If of uneven lengths, these pins will cause irregular spots in the casting. It now remains to describe the toggles used for operating the cores which form the holes through the three lugs in the casting. One of these toggles, of which there are three, is shown at I, in [Fig. 31], and also in [Fig. 32]. These toggles consist of brackets which are attached to the die-plate, and levers which are fulcrumed at the ends of the brackets so that their operation works the core pins. It is necessary to remove these core pins after each casting has been made and position them before another casting can be produced.
Fig. 40. Drilling the Ejector-pin Holes
The fitting of the parts of a die-casting mold is one of the most important parts of the work. It demands the highest type of workmanship, for a poorly fitted die means a die which works hard in addition to producing poor castings. It is very important that all movable parts should work freely. [Fig. 42] shows the assembling operation on a die-casting mold, the casting which is to be duplicated being shown in the immediate foreground. These parts must all be screwed into their respective places, making the joints as nearly air-tight as possible. One cause of poor die-castings arises from the trapping of air in the die, and different methods are employed for overcoming this trouble.