There is such a manufacturing process called custom brass casting, which involves pouring molten brass into a special mold to obtain metal parts that meet specific size, shape, and performance requirements. This article provides a full-process operation guide from design to finished product, which covers core parameters, alloy selection standards and solutions to common problems to ensure that you can directly use it for purchasing decisions or production planning.
01Core Process: How to Complete a Successful Customized Brass Casting
The following five steps must be strictly followed to obtain high-quality custom brass castings. A mistake in each step may lead to the scrapping of the final part or even substandard performance.
Step 1: Determine functional requirements and alloy selection
Before starting any design, it is important to understand the end-use environment of the part. This is the core decision-making process of the entire casting process.
The requirement for corrosion resistance is that if it is used for valves or marine hardware, you should choose C87850 (which is highly corrosion-resistant silicon brass) or C90500 (which is tin bronze).
For mechanical strength requirements that must withstand high pressure or heavy load, you should choose a material called C87850 or a material called C86300. The material here is manganese bronze, which has a tensile strength of more than 620MPa.
There are some requirements when performing machining, that is, for a large number of subsequent drilling and tapping operations, a material should be selected, that is, a free-cutting brass material of the C36000 type, which contains lead content to optimize chip breakage.
The requirement for surface treatment is that if electroplating or polishing is required, you should choose C87850 or C84400, which is half-red brass. When it is cast, its surface has smooth characteristics.
Step 2: Create a casting-grade 3D model
If the design drawing you provide is in STEP format or IGES format, it must be optimized for the casting process, rather than directly using machining drawings.
Key modification points :
Release slope (draft angle): All surfaces that are perpendicular to the parting surface must have a slope of 1° to 3° so that the casting can be taken out of the mold.
Rounded corners, also known as Fillet Radius, all internal sharp corners must be designed as rounded corners, and the fillet radius is at least R1.5mm to R3mm. The purpose is to prevent stress concentration and thermal cracking. This must be done.
Shrinkage Allowance: For brass, the solidification shrinkage rate is about 1.5% to 2.0%. For foundries, they will expand the model size during the mold design process to compensate for this shrinkage.
Step Three: Select Casting Process
Considering quantity and precision requirements, choosing the most suitable casting method is a decision that has a critical impact on cost and delivery time.
Step 4: Communicate technical specifications with foundry
Create a detailed request for quotation (RFQ) that must contain the following information:
1. Drawing documents : 3D models and 2D engineering drawings, with all key dimensions and tolerances marked.
2. The alloy designation clearly and accurately indicates the specific grade required by international standards, such as ASTM, EN, and JIS. For example, it is "ASTM B584-14 C87850".
3. Regarding quality requirements, what needs to be considered is whether X-ray testing, that is, RT, or penetrant testing, such as PT, is required, or whether pressure testing is required. Standard commercial-grade castings are generally inspected only for appearance and size.
4. The delivery state is in the as-cast state, which is called As-cast, and in the heat-treated state, or it has been machined, which is Pre-machined.
Step Five: Sample Verification and Production
First article inspection, also known as FAI, requires the foundry to provide the first article sample, and also attach a complete dimensional inspection report and material certificate, which is the Mill Test Report, or MTR for short. This report must list the measured values of all chemical components, such as Cu, Zn, Pb, Fe, Sn, Al, etc.
Instead of directly entering mass production, after confirming that the first piece is qualified, we will first start the production of 50 to 200 pieces for assembly and performance testing. This is small batch trial production.
02Design optimization rules: reduce defects and costs
By following these three core rules, casting defect rates and unit cost can be significantly reduced.
Rule 1: Avoid “Hot Spots”
Problem : Areas that are too thick can form isolated melt pools, causing internal shrinkage cavities.
The design plan is to ensure that the wall thickness is as uniform as possible when designing. If there are changes, use a gradual transition. Also, the ratio of wall thickness of adjacent sections should not exceed three to one.
A common case is that a valve manufacturer suddenly changed the wall thickness of the originally designed connection from 10mm to 30mm. This situation resulted in up to 50% of the castings being scrapped due to shrinkage cavities. After modifying it to a gradient slope condition with R20 fillets, the scrap rate was reduced to less than 3%.
Rule 2: Simplify the mold structure
Problem : Complex side core-pulling or recessed structures increase mold costs and extend lead times.
The solution is to modify the design to be as "open" as possible, avoid using sliders, or use subsequent machining to create complex features such as threaded holes and side keyways.
Adding a slider structure will increase the mold cost by an average of 35% to 50% and extend the mold production cycle by two to three weeks. This is supported by data.
Rule 3: Clarify the tolerance level
Problem : Too tight tolerances on non-critical features lead to a sharp increase in scrap rates.
The solution is to mark high-precision tolerances, like ±0.13mm, only for those dimensions that are critical for assembly. The solution is to use casting standard tolerances. For all other dimensions, such as CT8 grade, it is about ±0.5mm/25mm.
The impact of cost is to relax the tolerance from the precision level, marked CT6, to the commercial level, marked CT8. In this case, generally speaking, the price of a single piece can be reduced by 15% to 25%.
03Authoritative standards and verifiable information
All custom brass castings that meet the legal and technical basis for ensuring part reliability must comply with the following industry standards, all data derived from ASTM International (American Society for Testing and Materials) publicly released standards documents.
Core Materials Standards (ASTM)
ASTM B584 covers the chemical composition and mechanical property requirements of copper alloys (covering various types of brass) used for sand casting and permanent mold casting. This is the most common specification for cast brass.
ASTM B148 is specifically for aluminum bronze and silicon bronze castings. It is suitable for high-strength applications and high corrosion resistance applications.
ASTM B505 is for copper-based alloy continuous castings. It is suitable for the production of rods and pipes.
Mechanical property reference (based on ASTM B584 C87850 typical values)
Data source: ASTM B584-14 standard table X1.2. The specific measured value is based on the MTR of each batch provided by the foundry.
Common compliance certifications
There is such a situation, RoHS (2011/65/EU), which restricts hazardous substances (such as lead, mercury, etc.), and is specifically applied to parts of electronic and electrical equipment to be exported to the EU.
NSF/ANSI 61 is the health effects standard for drinking water system components. This standard applies to valves, faucets, brass castings, etc. that come into contact with drinking water.
ISO 9001 was established in 2015. It is the basic requirement of the quality management system of the foundry. It is not a product standard, but it can reflect the quality control capability of the factory.
04Frequently Asked Questions and Solutions (Q/A)
Q: What is the minimum order quantity (MOQ) usually?
A. Investment casting generally only accepts orders for 500 pieces. However, even for small batch production or prototype production, the minimum order quantity of 10 pieces can be achieved. As for sand casting, you only need one piece to start. However, the price of a single piece is quite high.
Q: How to determine whether the material certificate provided by the foundry is authentic?
A: The required report must be issued by a third-party laboratory (such as SGS) or an internal laboratory with ISO/IEC 17025 certification, rather than data printed out by yourself.
Q: My design has sharp corners, can it be cast?
A: No. Be sure to add rounded corners, otherwise thermal cracks or stress cracks will definitely occur at the sharp corners during casting, causing the parts to be scrapped.
Q: What is the typical lead time for custom brass castings?
A: Investment casting or sand casting takes two to four weeks to prototype. The production of a permanent mold or mass production mold takes six to eight weeks, with each subsequent batch taking one to two weeks.
Q: Why do brass castings rust (turn green)?
This shows the oxidation state of copper, not rust. If you want to maintain the golden appearance, you must ask the factory to do transparent spraying or electroplating nickel layer protection.
05Restatement of core ideas and suggestions for action
Core point of view: The success probability of customized brass casting depends on 90% of the understanding of the casting process during the design stage and the early technical communication with the foundry. Clarifying the alloy grade, optimizing the slope of the draft and the uniformity of the wall thickness, and pragmatically defining the tolerances are the only ways to avoid defects from the source, control costs, and shorten delivery deadlines.
Suggestions for action :
1. Execute immediately: According to the "design optimization rules" mentioned in Section 2 of this article, check the 3D model of the part you are currently operating on one by one, and make modifications to all places where there are sharp corners and sudden changes in wall thickness.
2. When preparing for an inquiry, you must determine a specific grade for your parts based on the ASTM standards listed in Section 3, such as C87850. Be careful not to just say "brass".
3. The verification process is that when issuing an inquiry to the foundry, they are required to clearly state the standard grade they will follow, that is, commercial grade or precision grade, and the declared grade must be written into the acceptance terms of the purchase order. This is a requirement of the entire process.
By following the standardized process stipulated in this guide, we can complete the entire closed-loop rhythm from conceptual design to the production of qualified parts, ensuring that your customized brass castings can meet the basic requirements of industrial levels in terms of mechanical properties, dimensional accuracy and cost efficiency.
