Monthly Archives: October 2017

WhatistheLostWaxInvestmentCastingProcess

Lost Wax Casting:
Lost wax casting is also called as investment casting and is one of the oldest technique carried out to obtain precision casting.
Today lost wax casting is widely used in each and every sector of casting so as to reduce machining cost and obtain fine surface finish.

What is The Process of Lost Wax Casting?
In lost – wax casting process wax pattern is coated with refractory ceramic material and ceramic material is hardened its internal geometry which takes the shape of the casting after that wax is melted out and molten metal is poured in the cavity.
The lost wax casting is divided in below mentioned departments for process control of castings.

  • Die/Mold making
  • Wax Pattern making
  • Wax pattern tree
  • Shell building
  • De-waxing
  • Shell firing
  • Casting
  • Refractory ceramic removal
  • Finishing

Die/Mold Making:-For making die it is very important to get perfect drawings of the specimen to get perfect die cavity as per norms

Wax Pattern Making :-After we get a correct die with perfect dimensions wax is injected in the die making is the replica of the final piece which is going to be casted.

Wax Pattern Tree:- Wax patterns dimensions are properly checked using Vernier caliper and are mounted on runner systems using sticky wax and finally it looks like wax pattern tree.

Shell Building :- After the wax pattern are completely stick on the runners they are properly inspected and then are dipped in refractory ceramic material and coated with zircon sand kept for drying and after a cycle of dipping coating and drying a thick layer is formed on the wax patterns which is called ceramic shell

Dewaxing:-After the shell is fully dried they are placed on shell stand and inserted in autoclave dewaxing machine and the wax is taken out from the shell at about 175°C which leaves the same cavity as the wax pattern inside the shell.

Shell Firing :- When the wax is removed from the shell. shell firing is done to remove the remains of the wax and increase the permeability of the shell.

Casting:- As the shell achieves a certain temperature in shell firing furnace the shell is taken out and placed on a sand bed and then the metal is poured in the cavity of the shell.

Refractory Ceramic Removal :- As the metal is cooled down after pouring in shell the shell is set to knocking machine to remove the refractory ceramic and get the final casted parts

Finishing :- the final castings are separated from the runner bars and further taken in machining department where finishing work like fettling, finishing is done of the casted parts. If needed certain heat treatments and surface treatments are given.

What are the Other Uses of Lost Wax Investment Casting Process?
Foundry-men and artists to make intricate sculptures, ornaments and automobiles widely uses the lost-wax casting process from decades. This process is also used for making casting brooches, jewelry, buckles and other small parts used in various industries.

What are the Advantages of the Lost wax Casting Process?
Despite modern ways of casting, foundry-men and artists still prefer the traditional methods of casting. Some of the advantages include –

  • The lost-wax casting process can be used on any material that can melt burn and evaporate to leave behind a mould cavity.
  • The duplicate model will reproduce even minute details of the original sculpture.
  • Allows for unique shapes of casting that would be impossible in other methods.
  • Near net shape castings are produced with high productivity and competitive price.

Hence, the lost wax investment casting process is a seasoned method for the reproduction of various objects.

However, the procedure does have its disadvantages such as the initial cost, need for large machinery and the particularity of holes in the mould. Therefore, it is important to look for expertise, design, performance and cost to get the best quality at the best price.

ComparisonofFilledandUnfilledPatternWaxes

Comparison of Filled and Unfilled Pattern Waxes

Filled and Unfilled Pattern Waxes:
Wax blends have been used for pattern making in Investment Casting process from decades. Initially the wax blends were unfilled or straight Pattern Waxes and they are blend of Paraffin Wax, Micro Crystalline Wax, Natural Waxes like Carnauba and resins, These waxes tends to shrink while solidification due to a pure wax blend.

The shrinkage of the Unfilled Wax is depend on wax temperature, tooling temperature, wax solidification rate and wax injection pressure.

To avoid the shrinkage of the heavy or thick cross section of wax patterns, wax chills are generally used, Wax chills are placed in to the wax cavity before wax pattern injection. These chills should be injected previously of the wax patterns and after Wax Pattern Production, there are chances of occurring chill marks on the wax pattern surface.

Filled Pattern Waxes are having different types of filler materials mixed in the base to avoid surface shrinkage defect also to accelerate the solidification.

Filler materials are solid cross linked polymer are in free-flowing powder condition and mix homogeneously with the base pattern wax.

While solidification of the wax patterns, Filled Patterns solidify fast compared to Wax Patterns produced by Unfilled Pattern Wax because it remain in solid form in the molten wax.

Filler Waxes are preferred for high productivity, better consistency and improved pattern quality and it has limitations of recycling.

Below mentioned are comparison of unfilled and filled pattern waxes,

Criteria Unfilled Pattern Wax Filled Pattern Wax
Simplicity in wax Pattern Production Proper wax conditioning must be done for proper wax pattern production Can be work with wide range of injection temperature
Productivity Unfilled waxes have low productivity because of higher cycle time Filled waxes have better productivity because of low cycle time and solid filler material content
Surface Sink / Dishing Chills must be used for thick cross sections to avoid surface sink / dashing Chills are not required for wide range of thickness as well
Flow Lines Flow lines / Non fill problems may occur due to minor changes in wax temperature No flow lines / Non fill problem and surface quality of wax pattern is good
Ovality and Shape sustaining Chances of ovality, Bending of wax patterns and variation in dimensions may occurs because of uneven cooling rates in variation of cross section Ovality, bending and variation in dimensions avoids due to 30 % to 40% of filler content, solidification of wax pattern mostly complete in the cavity during injection takes place
Process Control Close injection parameters, frequent inspection, process controlled and skilled operator required Wide range of inspection parameters, semi skilled operator, better reliability in dimensional consistency and quality required
Dewaxing and Burnt Out Maximum wax removal is possible while dewaxing and easy / fast burnt out while shell sintering Some quantity of wax tends to remain in the shell cavity after dewaxing also high temperature and longer time required for total burnt out
Recycling Recycling is easy after proper settling, filtration and centrifuge: ash content of used wax can be effectively removed Filled waxes could not be filtered or centrifuged due to filler content and There are limitations for ash removal (Only way to minimize ash content is by settling the wax at controlled temperature)

Considering all above features, Filled Pattern waxes are widely used in Investment Casting Industries, multi cavity dies and tooling can be easily used with Filled Pattern wax and it can be used for small wax pattern to large wax patterns.
Whereas Unfilled Pattern Waxes are used for small to medium size wax patterns.

Saffroshine Pvt. Ltd. is the leading manufacturer and supplier of water soluble waxes in across the world. Please connect with our wax expert for getting customized consulting solutions for your requirement at sales@saffroshine.com or call us at +91-217-2357272.