Frequently Asked Questions and Their Answers about Casting Foundry and CNC Machining:

Investment casting, which is also known lost wax casting or precision casting, refers to the formation of ceramic around the wax patterns to create a multi or single part mold to receive molten metal. This process utilizes an expendable injection molded wax pattern process to achieve complex forms with exceptional surface qualities. To create a mold, a wax pattern, or cluster of patterns, is dipped into ceramic material several times to build a thick shell. De-wax process is then followed by the shell dry process. The wax-less ceramic shell is then produced. Molten metal is then poured into the ceramic shell cavities or cluster, and once solid and cooled, the ceramic shell is broken off to reveal the final cast metal object. Precision investment castings can achieve exceptional accuracy for both small and large casting parts in a wide range of materials.
  • Excellent and smooth surface finish
  • Tight dimensional tolerances.
  • Complex and intricate shapes with design flexibility
  • Capability to cast thin walls therefore a lighter casting component
  • Wide selection of cast metals and alloys (ferrous and non-ferrous)
  • Draft is not required in the molds design.
  • Reduce the need for secondary machining. 
  • Low material waste.

During the investment casting process, a wax pattern is coated with a ceramic material, which, when hardened, adopts the internal geometry of the desired casting. In most cases, multiple parts are cast together for high efficiency by attaching individual wax patterns to a central wax stick called a sprue. The wax is melted out of the pattern – which is why it is also known as the lost wax process – and molten metal is poured into the cavity. When the metal solidifies, the ceramic mold is shaken off, leaving the near net shape of the desired casting, followed by finishing, testing and packaging.

Investment castings are widely used in pumps and valves, automobile, trucks, hydraulics, forklift trucks and many other industries. Because of their exceptional casting tolerance and exellent finish, the lost wax castings are used more and more. Especially, the stainless steel investment castings play a vital important role in the shipbuilding and boats because they have strong anti-rust performance.

According to the different binder materials used for making the shell, the investment casting could be divided into silica sol casting and water glass casting. The silica sol investment casting process have better Dimensional Casting Tolerances (DCT) and Geometrical Casting Tolerances (GCT) than water glass process. However, even by same casting process, the Tolerance Grade will be different from each cast alloy due to their various castability. Our foundry would like to talk with you if you have special request on the required tolerances. Here in the following are the general tolerances grade we could reach both by silica sol casting and water glass casting processes separately:
  • ✔ DCT Grade by Silica Sol Lost Wax Casting: DCTG4 ~ DCTG6
  • ✔ DCT Grade by Water Glass Lost Wax Casting: DCTG5 ~ DCTG9
  • ✔ GCT Grade by Silica Sol Lost Wax Casting: GCTG3 ~ GCTG5
  • ✔ GCT Grade by Water Glass Lost Wax Casting: GCTG3 ~ GCTG5

Sand casting is a tranditional but also modern casting process. It uses green sand (moist sand) or dry sand to form the molding systems. The green sand casting is the oldest casting process used in history. When making the mold, the patterns made of wood or metal should be produced in order to form the hollow cavity. The molten metal then pour into the cavity to form the castings after cooling and solidification. Sand casting is less expensive than other casting processes both for mold development and unit casting part. The sand casting, always mean the green sand casting (if no special description). However, nowadays, the other casting processes are also use the sand to make the mold. They have their own names, such as shell mold casting, furan resin coated sand casting (no bake type), lost foam casting and vacuum casting.

Thanks to our in-house capabilities and our out-sourced partners, we can proceed a diverse surface treatment. Available treatments include: polishing, zinc-plated, chome-plated, geomet, anodizing, painting...etc.

Sand castings are widely used in a diverse industries and mechanical equipment, especially for the large castings but with small demanding quantity. Due to the lower cost of development of tooling and pattern, you can invest a reasonable cost in mold. Generally speaking, the sand casting are the first choice for the heavy machineries such as heavy duty trucks, rail freight cars, construction machineries and hydraulic systems.

  • ✔ Lower Cost due to its cheap and recyclable mold materials and simple production equipment. 
  • ✔ Wide range of unit weight from 0.10 kg to 500 kgs or even bigger. 
  • ✔ Various Structure from simple type to complex type. 
  • ✔ Suitable for production requirements of various quantity.

Generally most ferrous and nonferrous metals and alloys could be cast by sand casting process. For ferrous materials, gray cast iron, ductile cast iron, carbon steel, alloy steel, tool steel along with the stainless steel alloys are most commonly poured. For nonferrous applications, most Aluminum, Magnesium, Copper-based and other nonferrous materials can be cast, while Aluminum and its alloy are the most widely cast via sand casting.

The casting tolerances are divided into Dimensional Casting Tolerances (DCT) and Geometrical Casting Tolerances (GCT). Our foundry would like to talk with you if you have special request on the required tolerances. Here in the following are the general tolerances grade we could reach by our green sand casting, shell mould casting and no-bake furan resin sand casting:
  • ✔ DCT Grade by Green Sand Casting: CTG10 ~ CTG13
  • ✔ DCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG8 ~ CTG12
  • ✔ GCT Grade by Green Sand Casting: CTG6 ~ CTG8
  • ✔ GCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG4 ~ CTG7

The sand molds mean the casting molding systems made by green sand or dry sand. The sand molding systems mainly cover the sand box, spures, ingates, risers, sand cores, mold sand, binders (if have), refractory materials and all other possible mold sections.

Shell molding casting is also called pre-coated resin sand casting, hot shell molding casting or core casting. The main molding material is the pre-coated phenolic resin sand, which is more expensive than green sand and furan resin sand. Moreover, this sand can not be recycle used. Therefore, the shell molding castings have higher costs than sand casting. However, compared to the green sand casting, the shell molding castings have many advantages such as higher dimensional tolerance, good surface quality and less casting defects. The shell molding casting process is specially suitable for producing castings of difficult shapes, pressure vessels, weight sensitive and castings requiring superior surface finishes.

  • Making Metal Patterns. The pre-coated resin sand needs to be heated in the patterns, so metal patterns are the necessary tooling to make shell molding castings. 
  • Making Pre-coated Sand Mold. After installing the metal patterns on the molding machine, the pre-coated resin sand will be shot into the patterns, and after heating, the resin coating will be molten, then the sand molds  become solid sand shell and cores.
  • Melting the Cast Metal. Using induction furnaces, the materials would be melted into liquid, then the chemical compositions of the liquid iron should be analyzed to match the required numbers and percents. 
  • Pouring Metal. When the melted iron meet the requirements, then they will be poured into the shell molds. Based on different characters of the casting design, the shell molds will be buried into green sand or stacked up by layers.
  •  Shot Blasting, Grinding and Cleaning. After the cooling and solidification of the castings, the risers, gates or additional iron should be cut off and removed. Then the iron castings will be cleaned by sand peening equipment or shot blasting machines. After grinding the gating head and parting lines, the finished casting parts would come, waiting for the further processes if needed. 
  • Shell-mould castings are generally more dimensionally accurate than sand castings. 
  • A smoother surface of the finished castings can be obtained by shell casting. 
  • Lower draft angles than sand castings are required by shell moulds casting. 
  • Permeability of the shell is high and therefore less or no gas inclusions occur.
  • Shell mold casting process needs very small amount of sand.
  • Mechanisation is readily possible because of the simple processing involved in shell moulding.
  • Cast Carbon Steel: Low Carbon Steel, Medium Carbon Steel and High Carbon Steel from AISI 1020 to AISI 1060. 
  • Cast Steel Alloys: 20CrMnTi, 20SiMn, 30SiMn, 30CrMo, 35CrMo, 35SiMn, 35CrMnSi, 40Mn, 40Cr, 42Cr, 42CrMo...etc on request.
  • Cast Stainless Steel: AISI 304, AISI 304L, AISI 316, AISI 316L and other stainless steel grade.
  • Cast Aluminium Alloys.
  • Brass & Copper.
  • Other Materials and Standards on request

• 2D drawings with dimension tolerances and/or 3D models which we can use for calculating the unit weight easily

• Material specification including heat treatment and required mechanical properties (if needed)

• Quality assurance expectations

• Special finishing/surface treatment requirements

• Tooling if required or existing

• Due date of quote response

• Application of the part you are asking

Before we make recommendations for the project and provide you with an offer, RMC firstly analyzes the following information to make our decision and proposals based on the request information you sent:

• Tooling requirements – best suited to scope of your project

• Quality expectations required to support your technical specifications

• Machining requirements

• Heat treatments

• Finishing requirements

• Expected date of delivery

Each alloy serves a difference purpose based on issues as diverse as heat exposure, run time, weight requirements, flexibility of the end product and so on. We work with you to determine exactly how your component need to perform and then guide you to the best alloy whether you need: Cast Iron, Cast Aluminum, Gray Iron, Cast Copper Alloy, Ductile Iron, Gray Iron, Cast Steel, Zinc Alloys, Stainless Steel and any other possible metal and their alloys.

Casting is one of the fastest and most cost effective methods for producing a wide range of components. However, to achieve maximum benefits, you’ll want to involve the cost analysis at an early stage of the product design and development. We have the expertise and experience to consult with you during the design phase so our engineers can help resolve issues affecting tooling and production methods, while identifying the various trade offs that could affect overall costs.

We have different casting types for your choice. Part of the optional process for your project will be the selection of the casting process. The most popular form is sand casting which involves making a replica of a finished piece (or pattern) that is compressed with sand and binder additives to shape the final part. The pattern is removed after the mold or impression has been formed, and the metal is introduced through a runner system to fill the cavity. The sand and the metal are separated and then the casting cleaned and finished for shipment to the customer.

Moreover, we also have the shell molding process produce the iron castings and steel castings. The shell molding is usually use resin coated sand for making molds.

Lead times with sand casting, investment casting, forging and machining vary due to part complexity and casting plant capacity. Generally 4-6 weeks is typical for tooling and sample castings and 5-7 weeks for production. Once a pattern is created, a component can be produced in seven days. For investment casting processes, much of this time is spent with the coating and drying of the ceramic slurry. While for sand casting, the time is mainly cost for the mold making. Investment casting facilities in RMC have quick drying capabilities for ceramic molds to produce parts in 24-48 hours. In addition, by using silica sol or water glass as bond material, engineered cast metal components can be delivered only several days after accepting a final CAD/PDF drawings or 3D models.

Investment castings can be produced in all alloys from decades of grams to hundreds of kilograms. Smaller components can be cast at hundreds per tree, while heavier castings often are produced with an individual tree. The weight limit of an investment casting depends on the mold handling equipment at the casting plant. The tree always should be significantly larger than the component, and the ratio ensures that during the casting and solidification processes, the gas and shrink will end up in the tree, not the casting.

Typically, a linear tolerance of ±0.005 in/in (0.127 mm/in.) is standard for investment castings. This would vary depending on the size and complexity of the part. Post-casting procedures, such as straightening or coining, often allow for tighter tolerances to be maintained on several specific dimensions.By working with our engineering staff, an investment casting drawing can be produced for a part that substantially reduces or completely eliminates the previous machining requirements to produce an acceptable component.

Because the ceramic shell is assembled around smooth patterns produced by injecting wax into a polished aluminum die, the final casting finish is excellent. A 125 rms micro finish is standard and even finer finishes (63 or 32 rms) are possible with post cast secondary finishing operations. Individual metal casting facilities have their own standards for surface blemishes, and facility staffs and design engineers/customers will discuss these capabilities before the tooling order is released. Certain standards depend on a component’s end use and final cosmetic features.

Due to the costs and labor with the molds, investment castings generally have higher costs than forged parts or sand and permanent mold casting methods. However, they make up for the higher cost through the reduction of machining achieved through cast near net shape tolerances. One example of this is innovations in automotive rocker arms, which can be cast with virtually no machining necessary. Many parts that require milling, turning, drilling and grinding to finish can be investment cast with only 0.020-0.030 finish stock. Further more, investment castings require minimal draft angles to remove the patterns from the tooling; and no draft is necessary to remove the metal castings from the investment shell. This can allow castings with 90-degree angles to be designed with no additional machining to obtain those angles.

To produce the wax mold patterns, a split-cavity metal die (with the shape of the final casting) will need to be made. Depending on the complexity of the casting, various combinations of metal, ceramic or soluble cores may be employed to allow for the desired configuration. Rapid prototypes (RP), such as stereo lithography (SLA) models, also can be used. The RP models can be created in hours and take on the exact shape of a part. The RP parts then can be assembled together and coated in ceramic slurry and burned out allowing for a hollow cavity to obtain a prototype investment cast component. If the casting is larger than the build envelope, multiple RP sub-component parts can be made, assembled into one part, and cast to achieve the final prototype component. Using RP parts is not ideal for high production, but can help a design team examine a part for accuracy and form, fit and function before submitting a tool order. RP parts also allow a designer to experiment with multiple part configurations or alternative alloys without a large outlay of tooling cost.

This depends on how well a metal casting facility make the gas out from the molten metal and how fast the parts solidify. As mentioned earlier, a properly built tree will allow porosity to be trapped in the tree, not the casting, and a high-heat ceramic shell allows for better cooling. Also, vacuum-investment cast components rid the molten metal of gassing defects as air is liminated. Investment castings are used for many critical applications that require x-ray and must meet definite soundness criteria. The integrity of an investment casting can be far superior to parts produced by other methods.

Generally most ferrous and nonferrous materials can be sand cast and investment cast. For ferrous materials, carbon, tool and alloy steel along with the stainless steel alloys are most commonly poured. Also, the rise in ductile iron casting demand has increased the use of the metal for sand casting and investment casting. For nonferrous applications, most Aluminum, Magnesium, Copper-base and other nonferrous materials can be cast, with Aluminum as one of the most common. Additionally, certain applications require the use of specialized other alloys used primarily in harsh environments. These alloys, such as Titanium and Vanadium, meet the additional demands that might not be achieved with standard Aluminum alloys. For example, Titanium alloys often are used to produce turbine blades and vanes for aerospace engines. Cobalt base and Nickel base alloys (with a variety of secondary elements added to achieve specific corrosion strength and temperature resistant properties), are additional types of cast metals.

• Main workflow: Inquiry & Quotation → Confirming Details / Cost Reduction Proposals → Tooling Development → Trial Casting → Samples Approval → Trial Order → Mass Production → Continuous Order Proceeding
• Leadtime: Estimatedly 15-25 days for tooling development and estimatedly 20 days for mass production.
• Payment Terms: To be negotiated.
• Payment methods: T/T, L/C, West Union, Paypal. 

Our factory located in Shandong, a province with rich manufacturing resources in China. We warmly welcome you to visit our factory and foundry at any time. It would be better if you can book the schedule with your service manager in RMC. You will have a nice trip with great achievments. 

For each casting batch, we will test the chemical composition of the molten metal before pouring. This is called Analysis of the Founding Furnace or On-the-spot Sample Analysis. For some special situation, this analysis should be done twice. Moreover, the chemical composition of the finished castings could also be tested for each batch by the spectometer. 

As we mentioned in the casting tolerance for sand castings, the shell mold castings have much higher accuracy and tighter tolerance than sand casting. Here in the following are the general tolerances grade we could reach by our shell mould casting and no-bake furan resin sand casting:
  • ✔ DCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG8 ~ CTG12
  • ✔ GCT Grade by Shell Mold Casting or Furan Resin Sand Casting: CTG4 ~ CTG7
Lost Foam Casting, also called Lost Foam Casting (LFC) or Full Mold Casting, is a kind of Evaporative Pattern Casting (EPC) with dry sand casting process. The EPC is sometimes could be short for Expendable Pattern Casting because the lost foam patterns could be used only once. After the foam patterns are finished by special machined, then the foamed plastic patterns are coated with refractory coating to form a strong shell to withstand the molten metal. The foam patterns with shells are put into the sand box, and fill it with dry sand sand around them. During pouring, the high-temperature molten metal makes the foam pattern pyrolyzed and “disappears” and occupies the exit cavity of the patterns, and finally the finished desired castings are obtained.
  • Greater design freedom for complex structural castings
  • No draft angle is needed to save lots of cost. 
  • Function integrated foam patterns could be assembled from several pieces of foam patterns.
  • Lost foam castings are near-net-shape process
  • High flexibility through short set-up times
  • Longer EPS mould service lives, hence lower proportionate tool costs
  • Assembly and treatment costs are reduced by the omission of the treatment process, installation parts, screw connections, etc.
  • Expansion of the scope of applications

Vacuum Casting is also known as Negative Pressure Sealed Casting, Reduced Pressure Casting or V Process Casting. Vacuum negative pressure casting is one type of dry sand casting and requires the use of air extraction equipment to extract the air inside the casting mold, and then use the pressure difference between the inside and outside of the mold to cover the heated plastic film on the patterns and the templates. The casting mold will become strong enough to withstand the molten metal during casting. After obtaining the vacuum casting mold, fill the sand box with dry sand without binder, and then seal the top surface of the sand mold with the plastic film, followed by vacuum to make the sand firm and tight. After that, remove the mold, put the sand cores, close the mold to make everthing ready for pouring. Finally, the casting is obtained after the molten metal is cooled and solidified.

  • The vacuum castings have high dimensional accuracy, clear outline and smooth surface.
  • There are no binders, water and additives in the molding sand, which makes the sand processing simple.
  • It is simple to clean the vacuum castings. Less harmful gases are generated during the casting process.
  • The vacuum castings could be used at a wide range of industries. It can be used for single-piece small batch production as well as mass production, especially large and medium-sized castings and thin-walled castings are more suitable for vacuum casting.

During vacuum casting, because the surface of the model is covered with plastic film, there is no need to vibrate or knock when pull the mold. The suction and negative pressure make the molding sand compact, and the hardness of the sand mold is high and uniform. Under the heat of molten metal, the cavity is not easy to deform. Moreover, the existence of negative pressure is conducive to the full filling of molten metal into the model. The surface roughness of V process castings can reach Ra = 25 ~ 2.5μm. The dimensional tolerance level of castings can reach CT5 ~ CT7. The appearance quality of negative pressure castings is good, and the internal quality is reliable.

CNC machining refers to the machining process proceed by Computerized Numberical Control (CNC for short). It is aided by the CNC to reach a high and steady accuracy with less labor cost. Machining is any of various processes in which a piece of raw material is cut into a desired final shape and size by a controlled material-removal process. The processes that have this common theme, controlled material removal, are today collectively known as subtractive manufacturing, in distinction from processes of controlled material addition, which are known as additive manufacturing.

The machining center is developed from the CNC milling machine. The biggest difference from the CNC milling machine is that the machining center has the ability to automatically exchange machining tools. By installing tools for different purposes on the tool magazine, the machining tools on the spindle can be changed by the automatic tool changer in one clamping to realize multiple machining features.

The CNC machining center is a high-efficiency automated machine tool that is composed of mechanical equipment and a CNC system and is suitable for processing complex parts. The CNC machining center is currently one of the most widely used CNC machine tools in the world with strong comprehensive processing ability. It can complete more processing content after the workpiece is clamped at one time. The processing accuracy is high. For batch workpieces with medium processing difficulty, its efficiency is 5-10 times that of ordinary equipment, especially it can complete Many processings that cannot be completed by ordinary equipment are more suitable for single-piece processing with more complex shapes and high precision requirements or for small and medium batch production of multiple varieties. It concentrates the functions of milling, boring, drilling, tapping and cutting threads on one device, so that it has a variety of technological means.