Checklist: Evaluating Porosity Control in Die Casting Quotes

A quote that lists “high quality” as a standard often hides a weak process. For procurement managers, the gap between a standard die casting and a reliable one usually appears in the porosity control plan. This checklist breaks down the quote into verifiable items. It helps you separate a supplier who manages the process from one who merely reacts to defects after they appear.

Process Controls in the Quote

The quote should specify how the supplier prevents porosity before the part is made. General statements about “good practice” do not provide enough detail. You need to see specific controls tied to the material and machine.

1. Melt Chemistry Verification: Look for a clause requiring the supplier to test the melt. For aluminum, this often includes checking silicon and iron content. For magnesium, sulfur levels matter. The quote should state that these tests happen before casting, not just after a batch fails.
2. Machine Parameter Locking: The quote should mention that critical machine parameters are locked or monitored. This includes injection pressure, injection speed, and hold pressure. If the supplier allows operators to adjust these settings freely, porosity risk increases. Ask for a record of these settings per batch.
3. Die Maintenance Schedule: Porosity often comes from a dirty die. The quote should reference a cleaning or maintenance interval. Look for language like “die cleaning after every X shots” or “daily die inspection.” Without this, the supplier may be relying on operators to notice problems manually.

Control Item	What to Look For in the Quote	Red Flag
Melt Testing	Specific elements tested, frequency of testing	“We follow standard melting procedures”
Machine Settings	Locked parameters or recorded data	No mention of parameter control
Die Maintenance	Defined cleaning frequency or interval	“Dies are maintained as needed”
Mold Temperature	Target temperature range specified	No temperature control mentioned
Mold Release	Type of release agent and application method	“Release is applied”

If the quote lacks these specifics, request a Process Flow Diagram. This document should map the sequence of operations from melting to finishing. It helps you see where porosity can enter the process.

Inspection and Verification Methods

Inspection is where porosity becomes visible. The quote must define what is checked, how it is checked, and what the limits are. “Visual inspection” is too vague for many applications.

1. Radiographic Inspection: For critical parts, ask if X-ray or gamma ray inspection is included. This method detects internal shrinkage porosity that visual checks miss. The quote should specify the coverage. Does it test 100% of parts, or only a sample? If it is a sample, what is the sample size?
2. Dye Penetrant Inspection: This is for surface-breaking porosity. It is cheaper than X-ray but only finds defects that break the surface. Ask if this is used for all parts or only after X-ray. It is often used as a secondary check for cosmetic or low-stress parts.
3. Ultrasonic Testing: For certain alloys and part geometries, ultrasonic testing can detect internal voids. This is less common than X-ray but useful for specific shapes. Check if the quote includes this method or if it is an extra charge.
4. Dimensional and Weight Checks: Sometimes porosity is caught by weight. A part with significant internal voids will be lighter than the theoretical weight. Ask if the supplier performs a weight check per lot. This is a low-cost, high-value check that should be in the quote.

The quote should also state who performs the inspection. Is it the supplier, a third-party lab, or your incoming inspection team? If the supplier handles it, request the inspection report format. You need a record that shows the part passed, not just a verbal confirmation.

Material and Melt Quality

Porosity is heavily driven by the quality of the melt. Gas porosity, in particular, comes from hydrogen dissolved in the metal. If the supplier uses low-quality scrap or does not degas the melt properly, the risk is high.

1. Scrap Management: The quote should define the source of scrap. Are they using recycled material from their own process, or is it purchased external scrap? External scrap can introduce contaminants and gas. Ask for a certificate of analysis for the scrap used.
2. Degassing Process: Look for a mention of degassing. For aluminum, this is often done with argon or nitrogen. For magnesium, vacuum degassing is common. The quote should state that degassing is part of the standard process. It should not be an option.
3. Inoculation: Some aluminum alloys require inoculation to improve solidification behavior. This reduces shrinkage porosity. Ask if inoculation is included in the price. If it is not, it may be an extra cost that affects the total.
4. Temperature Control: The melting temperature matters. If the melt is too hot, gas is more likely to form. If it is too cold, the fluidity drops and shrinkage increases. The quote should specify a temperature range for pouring.

If the supplier does not specify these material controls, they may be using a generic process. This works for simple parts but fails for complex geometries with thin walls or deep cavities. Ask for a material specification sheet that matches your part.

Documentation and Traceability

A quote without documentation is hard to enforce. If a defect appears in production, you need a paper trail. The quote should require the supplier to provide specific records for each lot.

1. Heat Traceability: Each batch of metal should be traceable to a heat number. This allows you to go back to the raw material if a defect appears. The quote should require this information on the packing list or inspection report.
2. Process Records: Ask for a copy of the machine parameter log for the specific production run. This shows the injection pressure, speed, and hold pressure used. If the parameters drifted, you can see it here.
3. Non-Conformance Reports: The quote should define how defects are handled. If a part fails inspection, does the supplier rework it, scrap it, or ship it with a waiver? The quote should state that defective parts are not shipped without your written approval.
4. Quality Plan: A formal Quality Plan should be available for review. This document outlines the supplier’s system for preventing defects. It should include control charts for key parameters. If the supplier refuses to share this, it is a sign that they do not have a structured quality system.

Without these documents, you are relying on trust. In procurement, trust is not a control. You need records that prove the process worked as intended.

Red Flags in the Quote

Some language in a quote signals weak porosity control. Watch for these phrases and ask for clarification.

• “Best effort” or “industry standard”: These are vague. They do not define what the supplier will do. Ask for the specific standard or method they are referring to.
• “Inspection included” without method: This could mean a visual check by a technician. It does not guarantee X-ray or ultrasonic testing. Clarify the method and coverage.
• “No warranty on internal defects”: This is a major red flag. It means the supplier will not take responsibility for internal porosity. For most die cast parts, internal defects are a quality failure, not a cosmetic issue.
• “Price excludes special inspection”: If X-ray or ultrasonic testing is always excluded, it is not a special service. It is a standard requirement for quality. Ask why it is not included.
• No mention of melt chemistry: If the quote does not mention testing the metal, the supplier is not controlling the primary cause of gas porosity. This is a significant gap.

Negotiating the Quote

When you identify gaps, do not just add clauses. Ask the supplier to explain their current process. Sometimes the quote is generic because the supplier has not customized it for your part.

1. Request a Process Review: Ask the supplier to walk you through their process for similar parts. This helps you understand their capabilities. If they cannot explain how they prevent porosity, they may not have a process.
2. Define Acceptance Criteria: Be specific. “No porosity” is not measurable. Define the size and location of acceptable porosity. For example, “No porosity larger than 1mm in the load-bearing area.” This gives both parties a clear standard.
3. Include Penalties or Credits: If the supplier has a history of porosity issues, include a credit or penalty for rejected lots. This aligns their incentives with your quality goals. It does not need to be large, but it should exist.
4. Require a Pilot Run: Before committing to a large volume, request a pilot run with full inspection. This verifies that the process works in practice. It also gives you data to negotiate future terms.

A strong quote is a statement of control. It shows the supplier has thought about where porosity can come from and how they will stop it. If the quote is vague, the process is likely vague too. Use this checklist to force specificity. It will help you buy quality, not just parts.