cad.ppt

APRESENTATION

ONRAPID TOOLING

By:AKANT KUMAR SINGH

10M318(CAD/CAM)

INTRODUCTION The term Rapid Tooling is typically used to describe a

process that either uses a rapid prototyping model as a pattern to create molds quickly or uses the rapid prototyping process directly to fabricate tools for a limited volume of prototypes.

The most RT approaches utilizes multi step procedures involving a mixture of RP processes and conventional tool fabrication methods.

CLASSIFICATION OF RT ROUTESRapid tooling techniques have been classified in

various ways,1.Soft/Bridge/Hard tooling2.Nondirect/Direct tooling3.Prototype/Bridge/Production tooling

Soft tooling refers to tools required for small quantity production. Hard tooling is the opposite, refer to tools required for large quantity production.

The bridge tooling is somewhere in between the both or in other words it refers to tools required for medium quantity production.

In view of the small production quantities, tooling cost reduction is of prime importance.

In contrast to hard tool steel used in hard tooling, soft tooling is usually produced from soft materials such as silicon, rubber, epoxies, zinc alloys, aluminum etc.

Much hard tooling in industry is produced by means of computer numerical control machining (CNC) and electrical discharge machining (EDM).

Soft tooling can be used in processes such as injection and compression molding, blow molding, vacuum casting and forming.

Many RP technologies, including stereo lithography (SL), are applicable in the fabrication of soft as well as hard tooling.

Many RT routes utilize a master pattern with a view to fabricating the final production tool by methods such as investment casting.

These type of RT routes are called Indirect as they include at least one intermediate step in the tooling process.

In Direct tooling , no intermediate steps are involved in the manufacture of tools.

As the stereolithography apparatus directly provides the prototype, these techniques can directly supply the production tool.

RP OF PATTERNSA critical element of any casting technology,

conventional or otherwise is the master pattern. Many times the pattern is of complex geometry with fine detail.

With the advent of RP processes capable of creating patterns, many industries have applied investment casting and precision casting for the fabrication of rapid production tooling.

The RP approaches used to pattern making include SL, Selective laser Sintering, laminated object manufacturing and 3D printing.

Conventional investment castings are produced by the

solid mold method or the shell casting method.

Shell molding utilizes patterns made of wax, so they can be melted away. The patterns are produced from female cavity dies and assembled on a common gating system. The assemblage is called a cluster.

When the shell is complete, the wax invested within is removed by placing the shell in a preheated furnace.

Molten metal is then poured through the runner or sprue system under gravity, pressure and vacuum.

INDIRECT RTThe indirect method uses RP master pattern to produce a

mold. Silicon rubber molding and epoxy tooling are some examples of indirect methods.

There are various indirect methods for soft and bridge tooling. some of these are:

1. RTV-SRM(Room temperature vulcanizing silicon rubber molds)

2. Nickel Ceramic Composite (NCC) tooling3. Composite aluminum filled epoxy (CAFE) tooling 4. Rapid mold process

Nickel Ceramic Composite ToolingThis is indirect approach applicable to rapid bridge tooling

for injection molding is the use of ceramic composite tooling.

In this tooling, the hard active surfaces of the mold are made of electroformed nickel backed by a high-strength ceramic.

The advantages of using nickel include good thermal conductivity, corrosion resistance and polishing ability.

The nickel shell, ceramic backing, and containment unit move together during injection molding.

Steps involved in NCC tooling1. The process starts with the definition of the parting

surface from the CAD model of the part.

2. The parting surface is then expanded in a linear fashion in the z-direction to determine the geometry of a Single integrating matching plate electroforming (SIMPLE) tool model.

3. The amount of z-expansion is set to ensure good stability during subsequent electroforming.

4. Next, the nickel shells are electroformed on the simple mandrel using conditions favoring good stability.

5. The mandrel with electroformed nickel on both sides is next attached to the mold frame using a set of clamp-ring buss bars.

6. Next, the ceramic is vacuum cast through a small opening in the back of the mold frame.

7. Some post-processing may be necessary for creating holes for ejector pins. Nickel is softer than most tool steels.

Indirect methods for Production toolingTooling enabling normal production quantities is called

production tooling. It means that production tooling must be much more durable than soft and bridge tooling.

A widely used indirect RT process for production tooling is a powder based metal process called 3D keltool.

3D keltool is recognized as an extremely fast method of producing hard tool inserts for injection molding or die casting.

Many companies use the method to produce thousands of parts.

The process starts with a CAD design of the core and cavity mold inserts, followed by the creation of the core and cavity patterns by means of SL.

Next, the pattern is finished, polished to the desire surface and silicon rubber is cast against them to create molds.

When the SL master is taken out of the rubber mold, it leaves behind the negative pattern corresponding to the master.

A mixture of A-6 powder steel slurry & a binder is poured into the soft mold.

Once the slurry has settled into the rubber and hardened, the insert is taken out and placed in a furnace so as to melt the binder out and bring the insert to a green state.

The pattern with the low melting point is then easily removed by heating the green compact.

Keltool is capable of producing tool inserts with tolerances of the order of 50µm. Through appropriate heat treatment, the inserts can be hardened.

Investment Cast ToolingInvestment casting has been used with RP models to

produce metal tooling. Traditional methods of investment casting with injection molding is compared with investment casting using RP.

Most of the tools are cast from aluminum, but some steel molds have also been used.

The lost wax process can be used to replicate the part in metal by first making a sacrificial RP model of the desired cavity.

The RP pattern is first invested in multiple layers of ceramic slurry, which are allowed to dry between coats. After the shell has dried, the ceramic shell and invested part are fired.

The firing process sinters the ceramic shell and causes the invested model to burned out. After firing, any ash residue is washed away from the ceramic shell.

The molten alloy of the tool material is then poured through a gating system into the void left by the RP pattern.

After solidification and cooling, the ceramic shell is fractured and the newly formed metal cavity is removed and postprocess machined.

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