“We machined it exactly according to the drawing, but the dimensions are off,” “The cut surface is peeling and won’t pass visual inspection,” “Porosity appeared after machining, and the whole batch had to be scrapped”—.
Along with the rising need for weight reduction, the demand for aluminum parts—from automotive components to electronic device casings—is increasing every year. According to statistics from the Japan Aluminium Association, demand for aluminum rolled products remains solid, with the transport machinery sector accounting for about 40% of the total, making it a key field. However, while aluminum is said to be “light and easy to machine,” it is also a “difficult material to handle” that can invite serious machining troubles if its physical properties are not deeply understood.
In this article, we will focus on “5 representative failures” in aluminum processing that frequently occur on the manufacturing floor, thoroughly explaining their technical causes and specific avoidance strategies. Furthermore, we will touch upon the key points of “high-quality aluminum procurement in Vietnam,” which has recently garnered attention as a means to simultaneously realize cost reduction and supply chain resilience. We deliver practical information for executives and procurement managers who wish to prevent cost increases due to quality troubles and review their procurement strategies.
The Physical Reasons Why Aluminum Processing Is “Surprisingly Difficult”
Before getting into specific failure examples, let’s understand the root causes of why troubles occur in aluminum processing through numbers. When compared to iron (such as SS400), aluminum (such as A5052 or ADC12) has three distinct characteristics that make processing difficult.
- Large coefficient of thermal expansion: Aluminum’s coefficient of linear expansion is approximately 23.6×10⁻⁶/°C, which is about twice that of iron (approx. 11.7×10⁻⁶/°C). Dimensional changes due to machining heat are severe, causing it to shrink and fall out of tolerance when it cools.
- Low melting point: While iron’s melting point is approx. 1,538°C, aluminum is approx. 660°C, less than half. The material melts easily from cutting heat, causing “welding” (adhesion).
- Low Young’s modulus (rigidity): Aluminum’s Young’s modulus is approx. 70GPa, which is about one-third that of iron (approx. 206GPa). In other words, under the same force, it deforms three times more easily than iron, making “distortion” due to chucking (clamping) or cutting resistance more likely to occur.
Setting machining conditions while ignoring these characteristics leads to the following five failures.
Failure 1: The Trap of “Thermal Deformation” Where Dimensions Don’t Match
Cause: Accumulation of Machining Heat
The most common trouble is the case where “it was within dimensions during machining, but fell out of tolerance when returned to room temperature.” As mentioned earlier, aluminum expands with heat twice as much as iron. For example, if a 100mm long aluminum part rises by 50°C due to machining heat, it expands by approximately 0.118mm by calculation. This is a fatal error for precision parts.
Avoidance Strategy: Temperature Management and Coolant
- Use of water-insoluble cutting oil: For finishing, select water-insoluble cutting oil that has high lubricity and suppresses frictional heat.
- Separation of roughing and finishing: Perform finishing after setting aside “dwell time” to cool down the heat generated during roughing.
- Appropriate cutting speed: While high-speed machining is possible with aluminum, it is effective to use carbide tools and maintain an appropriate peripheral speed of 300m to 800m per minute (depending on the material), adopting a strategy to remove heat with the chips before it accumulates.
Failure 2: “Built-up Edge (Welding)” Roughening the Finished Surface
Cause: Material Adhesion
Aluminum has high affinity, and chips tend to weld to the cutting edge of the tool, forming a “built-up edge.” When this falls off, it damages the machined surface (tear-out/galling), worsening surface roughness. This is particularly noticeable in wrought materials like pure aluminum (A1000 series) and A5052.
Avoidance Strategy: Tool Selection and Lubrication
- Tools with large rake angles: Prioritize sharpness and use chips with a positive shape (rake angle of 20° or more recommended).
- DLC coating: Diamond-Like Carbon (DLC) coated tools have a low friction coefficient of 0.1 or less, dramatically preventing aluminum adhesion.
- Increasing coolant supply pressure: Supply coolant at high pressure to forcibly evacuate chips.
Failure 3: “Distortion and Chatter” in Thin-Walled Workpieces
Cause: Excessive Chucking Force
Since aluminum has low rigidity, it deforms just by the fixing force (clamping force). When the clamp is removed after machining, the material tries to return to its original shape due to elastic recovery, resulting in compromised flatness or roundness.
Avoidance Strategy: Low-Stress Fixturing
- Management of tightening torque: Use a torque wrench and fix with the minimum necessary force.
- Shaping of soft jaws: Machine soft jaws to match the shape of the workpiece, increasing the contact area to hold by surface, thereby lowering local pressure.
- Vacuum chuck: For thin plate machining, the method of fixing by suction using air pressure is effective.
Failure 4: “Internal Defects (Porosity/Blowholes)” Discovered After Machining
Cause: Gas Entrapment During Casting
This is a problem specific to and the largest issue with aluminum castings (die casting). Even if the exterior is beautiful, the moment the inside is shaved off during cutting, “voids (cavities)” appear, leading to defective products due to airtightness leakage or insufficient strength. In die-cast materials like ADC12 specifically, the occurrence rate can reach several percent to 10%.
Avoidance Strategy: Casting Process and Impregnation Treatment
- Vacuum die casting method: Reduce pressure inside the mold before injecting molten metal to reduce gas entrapment.
- Impregnation treatment: After machining, resin is infiltrated into minute voids using vacuum pressure and hardened to ensure airtightness. Designing with this process in mind is important.
Failure 5: “Scratches and Dents” During Secondary Processing
Cause: Underestimating the Softness
Aluminum (especially pure aluminum or non-heat-treated alloys) has low surface hardness, and marks may remain even if pressed with a fingernail. Cases where parts touch each other during washing, transport, or packing after machining, causing dents and resulting in appearance defects, are never-ending.
Avoidance Strategy: Dedicated Returnable Containers and Education
- Individual packaging: Use dedicated dividers (returnable containers) so that parts do not touch each other within the pallet.
- Handling education: Thoroughly instill the mindset in the workplace to “handle aluminum like a raw egg.”
The Solution of Vietnam Procurement: Balancing Cost and Quality
How can cost reductions be achieved while clearing the technical challenges mentioned above? Currently, many Japanese companies are paying attention to “Vietnam.”
Why Vietnam?
According to a survey by JETRO (Japan External Trade Organization), about 60% of Japanese companies operating in Vietnam have achieved profitability, and the evaluation as a procurement destination in the manufacturing industry is rising every year.
- Cost merit: Labor costs are about one-quarter of Japan’s and about half of China’s. This makes it possible to perform labor-intensive processes such as deburring and total inspection carefully while keeping costs down.
- Young and diligent workforce: The average age of Vietnamese people is in the early 30s, and their national character of being dexterous and serious is suitable for aluminum processing and inspection tasks that require precision.
- Diversification of country risk: As a leading candidate for “China Plus One,” it is optimal for diversifying supply chain risks.
Integrated Production from “Casting to Machining” Is Key
The biggest point to avoid failure in overseas procurement is to complete “casting (die casting)” and “cutting (machining)” within the same factory (or the same supplier).
If orders are placed with separate companies, when defects due to porosity occur, a blame game of “the casting is bad” vs. “the machining position is bad” often tends to occur. If you choose a supplier like Daiwa Aluminum Vietnam that can provide a one-stop service from casting to machining and surface treatment, quality responsibility becomes clear, and the total lead time is also shortened.
Summary
Aluminum processing failures stem from a lack of understanding of material properties (thermal expansion, adhesiveness, low rigidity) and inappropriate process management.
- Thermal deformation measures: Temperature management and appropriate coolant
- Welding measures: DLC coated tools and lubrication
- Distortion measures: Low-stress chucking
- Porosity measures: Vacuum die casting and impregnation treatment
- Dent measures: Careful handling
While implementing these technical measures requires appropriate equipment and man-hours, by utilizing excellent suppliers in Vietnam, it is possible to achieve both “Japanese quality technical management” and “Vietnamese cost competitiveness.”
As the next move for cost reduction and quality stabilization, why not consider partnering with a trusted Vietnamese partner? Daiwa Aluminum Vietnam will powerfully support the solution of your challenges from the local site.