Aluminum die casting

Introduction to Aluminum Die Casting

Aluminum die casting is the most common process to produce aluminum casting parts used in diverse industries. As aluminum has excellent material flowability, highly corrosion resistant, and high dimensional stability with complex parts shape.

 

Meanwhile the aluminum die casting part is high mechanical strength, easy to cast, and lower cost compared to zinc or magnesium die casting parts.

Aluminum die casting parts have very good physical properties that withstand high temperature. which makes aluminum casting could be used in automotive, airplane, medical, and other industrial products.

 

Aluminum die casting process requires to use cold chamber die casting machine with high pressure, during the aluminum die casting process, the raw aluminum material is molted in a furnace that set aside of die casting machine. Then the molted material is transferred from furnace to die casting machine by a ladle. After that, those material will be forced into the die casting mold cavity where the material is solidified to obtain desired die casting products.(A die casting mold tool can normally last for 800,000~150,000 shots)

Aluminum Die Casting Terminology

Zinc Die CastingAluminum — One of the most commonly used die casting metal material with lightweight, cheap cost, and silver color(raw material color).

 

Aluminum Die Casting Process— A metal die casting process that normally requires to use a cold chamber die casting process that raw material is molten in an furnace which is set aside of die casting machine, then it’s poured into die casting machine by a ladle. After that, the molten material will be transferred into mold tool where the material cools and solidifies to become the desired die casting parts.

 

Castability — The capability of a material that be used for die casting process.

 

Die Casting Machine: A electro-mechanical device for die casting process that particularly consists of mold clamping system, material melting, material injection, and part ejection system. For different melting system, a die casting machine can also divided into cold chamber machine and hot chamber machine. Normally aluminum die casting process use a cold die casting chamber machine; zinc and magnesium use hot chamber machine.

 

Cold Chamber Machines—  Because aluminum has a relative higher melting point, It particularly requires the raw material should be pre-melted by furnace that set aside of die casting machine, instead of material is melted inside a die casting machine.

 

Die Casting Mold Tool:  A steel tools where the molten material cools and solidifies to form a die casting part. It’s made of hardened steel(HRC48°C~ HRC52°C), with two different plates as core side and cavity side, sliders(if needed).

 

Mold Core — A part of mold plate where is the outstanding feature of same shape as final die casting part. It normally attached with ejection system to fall of part.

 

Mold Cavity — A part of mold plate where is the recessed feature of same shape as final die casting part. It normally connects with gate and runners.

 

Clamping Force —It is used to keep mold tool closed tightly when material injection process. The force is originally generated by the hydraulic cylinder of die casting machine.

Draft

 

Parting Line —It looks like a small flash line that left by the fitting area of mold core and cavity after die casting process.

 

Draft — A linear angle existing in the cavity and core side of mold tool so as to enable die casting part depart from mold tool easier.

 

Slide — A movement structure in the mold tool to realize the special features that a normal cavity and core can’t form.

 

aluminum die casting partsOverflow — It’s an additional runner attached to die casting part, so as to filter some material defects like bubble or combined material.

 

Runner — The material flowing channel in the die casting mold starts from sprue to die casting part.

 

Sprue — A round hole in the die casting die mold that the molten metal starts from it until die casting part.

Vent — A small space between the fitting surface of cavity and core, used to release high pressure and air when material injection process.

 

Rib — A thin wall that used to enhance part strength.

 

Finishing — It refers the surface treatment to meet using requirements, like electro-plating, anodizing, powder coating, printing, etc.

 

Shrinkage— A small recessed features from part surface when molten material cools and solidifies.

 

Shrink Mark— The recessed mark that left by material shrinkage.

 

AQL— A quality acceptable standard for quality control. It’s originally used in US military system.

 

CPK — It’s a quality control index that generated by statistic process of a series inspection data. By checking CPK data, we can visually observe our manufacturing stability and tendency.

 

Benefits of Aluminum Die Casting:

  • aluminum castingHigh dimensional stability for complex shapes
  • Closed to tolerance after a part is die-casted, as it only needs less machining process.
  • Very good strength and hardness properties
  • Good heat dissipating properties
  • High operating temperatures
  • Outstanding corrosion resistance
  • Could be thin wall and lightweight
  • Good stiffness and strength-to-weight ratio
  • Excellent EMI and RFI shielding properties
  • High thermal and electrical conductivity
  • Good finishing characteristics
  • Fully Recyclability
  • Non-magnetic

Aluminum Material Profile:

  • Density: 2.702 g/cm3
  • Melting Point: 660.37 °C – 933.52 °K
  • Boiling Point: 2467.0 °C – 2740.15 °K
  • Number of Protons/Electrons: 13
  • Number of Neutrons: 14
  • Crystal Structure: Cubic
  • Natural Color: Silvery or white

 

Die Casting Process Simulation and Analysis

Hammer Motion Simulation

We utilize professional casting analysis software(Cast-Designer) to study the speed and switching point of high-pressure casting process, it is beneficial to reduce the oxides and gases that brought into the mold cavity. The simulation can clearly anticipate any injection issue during the first-second speed of the hammer in the injection tube, and understand how the molten metal flows in the pressure chamber.

Material Filling and Venting Simulation

With professional simulation software, we can accurately simulate the filling and air exhausting process of various die-casting alloys, and accurately determine the area where the gas is exposed and the exhaust gas is not smooth. In addition, “Gas Lead Time” and “Maximum Volume Pressure” can be used for accurate single-graph risk viewing.

Solidification and Shrinkage Simulation

Through the simulation of the solidification process, the isolated liquid phase and the risk area of ​​the shrinkage can be accurately realized. In general, the isolated liquid area is also the hot junction region, where is easier to form shrinkage since there is no material compensation channel.

Mold Temperature Analysis

The mold temperature of high pressure casting process can keep stable when the first 10~100 pcs of products. However it might change a lot when more production. We use software to find out whether the mold is overheated or too cold, which can predicate the casting defects accurately.

The Flow-chat of Aluminum Die Casting

The-Flow-Chat-of-Aluminum-Die-Casting-Process

The Process of Aluminum Die Casting

Die casting machine, aluminum raw material, and die casting mold tool are the three basic factors to produce a die casting parts. For an aluminum die casting process, it particularly requires to use a cold chamber casting machine under a high pressure.

During the aluminum die casting process, the raw aluminum material is pre-molted in a furnace that set aside of die casting machine. Then the molted material is transferred from furnace to die casting machine by a moveable ladle. After that, those material will be forced into the die casting mold cavity where the material cools and solidifies to obtain desired die casting products. Here below are the process step breakdown.

 

Step 1. Material Melting

Since aluminum has a very high melting point(660.37 °C) that can’t be melted inside a die casting machine directly. This is why we need to pre-melted it with a furnace that attached with a die casting machine.

 

Step 2. Mold Tool Mounting and Clamping

It’s almost similar to injection molding, the die casting process also needs a mold tool for casting process. Therefore we need to mount the die casting mold tool on a cold die casting machine.

 

Step 3. Injection or Filling

The molten material is transferred from furnace to die casting machine by a moveable ladle. In this stage, the material will be poured and forced into the die casting mold cavity where the material cools and solidifies to obtain desired die casting products.

 

Step 4. Cool and Solidification

After the die casting mold tool is fully filled with molten material, it takes 10 ~50 seconds to cool and solidify( it depends on part structure and size).

 

Step 5. Part Ejection

When the mold opens, the casted parts would be ejected off by ejection pins from die casting mold tool. Then the raw casted parts is ready.

The 4 Key Factors in Die Casting Process

Die Casting is a repeatable and consistent metal parts manufacturing process. it consists of die casting machine, mold tool, and metal material. However a die casting process can also break into four main parameters as pressure, speed, temperature, and time. A good die casting process must combine those parameter properly. Here below we would like to introduce the main parameters of a cold chamber die casting machine:

 

Pressure

The pressure parameter is set to minimize the working pressure under the premise of ensuring that the machine can work normally without affect product quality. Here below are some consideration for pressure setting.

 

1.    For Different Parts Structure

  • A relative higher pressure utilized for thin wall of part; and a lower pressure will be used for thick wall of parts.
  • A simple part structure requires lower pressure; and a complex part structure will utilize high pressure.
  • A lower pressure used for those parts with optimized die casting process, like proper draft, ribs, rounds, and thickness.

 

2.    For Different Material Properties

  • The crystallization temperature of material ranges larger, and the higher pressure is needed; if opposite, the lower pressure will be better
  • .If a material with better flowability requires less pressure, if opposite, the higher pressure will be used.
  • The higher density of material requires higher injection pressure; the lower density material will utilize lower pressure.

 

3.    For Different Gating System

  • If the runner resistance is larger, the pressure ratio should be also higher.
  • If the temperature of gating system can be quickly exhausted, it requires lower pressure. If opposite, the higher pressure will be used.

 

4.    For Different Venting System

  • A big enough of air exhausting system requires lower pressure.
  • More reasonable air exhausting system needs lower pressue.

 

Speed

 

The injection speed can be divided into a slow injection speed (also known as the first speed of the shot), a fast shot speed (also known as the second speed of the shot), and a supercharged speed.

 

The slow injection speed is usually selected in the range of 0.1-0.8 m/s, and the moving speed is gradually increased from 0. The fast injection speed is proportional to the in-gate speed, generally adjusted from low to high, without affecting the quality of the casting. it is better to use a lower fast injection speed, that is, an in-gate speed.

 

The pressurization movement takes a very short time, and its purpose is to compact the metal and make the casting compact. When the supercharging movement speed is adjusted, it is generally observed that the pressure indication value of the injection pressure gauge rises uniformly in a slanting line during the supercharging movement, and the die-casting product can be free from looseness.

 

Per our experience, the speed adjustment can be set up based on following principles:

  • If the mold temperature is low, we will use lower injection speed. If opposite, we have to use high speed.
  • A complex part structure requires high injection speed.
  • A vertical gating system will normally use a speed of 15~25 m/s
  • A horizontal gating system will normally use a speed of 20~35 m/s
  • A thin wall(less than 3.0mm) of part thickness will normally utilize 38~46 m/s
  • A thick wall(more than 5.0mm) of part thickness will normally utilize 27~47 m/s

 

Time

  • Injection Time: The injection time is proportional to the wall thickness of the casting part. For the large part, the injection time required longer since the injection volume is big and injection process is slow.

 

  • Mold Opening Time:The mold opening time generally takes over 2 seconds. However a thicker die-casting part needs more time than a thinner part; and the complicated mold structure requires a longer open time than the simple mold.

 

  • Ejection Delay Time: Under the premise of ensuring that the product is fully solidified and not sticking, it’s necessary to reduce the ejection delay time (it’s generally over 0.5 seconds).

 

  • Ejection System Return Time: To ensure the die casting parts can be taken out from machine, we should keep enough time for this movement before a mold tool closed. (it’s generally over 0.5 seconds).

 

Temperature

1.    Alloy Casting Temperature

The alloy casting temperature is the average temperature at which the molten metal enters the mold cavity from the pressure chamber. Due to the inconvenience of measuring the temperature of the liquid metal in the pressure chamber, it is usually expressed by the temperature in the holding furnace.

Here below are the furnace temperature reference for common casting process

  • Aluminum Alloy: 610 °C.~700 °C.
  • Zinc Alloy: 410 °C.~450 °C.
  • Magnesium Alloy: 640 °C.~700 °C.

If the pouring temperature is too high, the alloy shrinks greatly, the die casting is prone to cracks, and the die castings have coarse grains and can cause brittleness;

If the pouring temperature is too low, defects such as cold partition, surface flow and insufficient pouring may occur. Therefore, the casting temperature should be considered along with the pressure, mold temperature and filling speed. In order to last a longer mold life, we should try to use as lower mold temperature as long as the shrinkage issue does not come up.

 

2.    Die Casting Mold Temperature

Prior to a die casting process, the die-casting mold should be preheated to a constant temperature before use, and should be kept within a certain temperature range during the production process. The die casting mold temperature will effect on the temperature, viscosity, fluidity, filling time, and filling flow state of the molten metal.

Here below are the mold temperature reference for common casting process

  • Aluminum Alloy: 220 °C.~280 °C.
  • Tin Alloy: 60 °C.~120 °C.
  • Zinc Alloy: 160 °C.~200 °C.
  • Magnesium Alloy: 200 °C.~250 °C.
  • Copper Alloy: 300 °C.~350 °C

Our Aluminum Die Casting Service

Eco Die Casting company is one of the leading precision aluminum die castings manufacturers in China, We are dedicating to providing customers high quality casting products while keeping their cost with very economical manufacturing solution.

 

As our facilities were certificated with ISO 9001-2008 and TS16949 quality system, it enables us to provide clients high quality products in accordance with international quality standard, and ship the products to worldwide customers from our factory.

diemold-1image of die casting mold makingproduct

We are capable of producing both high quality die casting parts and die casting mold tools. Our main capabilities can be breakdown as below:

 

  • Aluminum alloy material we use: A356, A360, A380, A383 A413; ADC1, ADC3, ADC6, ADC10, ADC12;  ZL102, ZL104, AlSi12, YL104, YL112,  YL113
  • Secondary Process: CNC machining, drilling, tapping, assembly, etc
  • Surface Treatment: Electro-plating, powder coating, polishing, sand blasting, heat treatment, painting, anodizing, chrome plating are available
  • Die Casting Mold Material: H13, NAK55, NAK80, SDK61, S136, LKM2344, LKM718, etc
  • Mold Base Brand: LKM(China), DME, EMP, Hasco, MISUMI
  • Mold Life: 80,000~150,000 shots
  • Tolerance Standard: +/-0.005mm
  • Part Weight: 30 gram~15KG
  • Die Casting Machine Tonage: 120T~1650T
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