DFM (Design for Manufacturing) is an effective communication tool between the customer and the mold maker. It visualizes the most basic information about the injection mold and the plastic parts it will produce, so it is much easier to discuss whether the part or mold design can be further optimized.
DFM (Design for Manufacturing) is an efficient communication tool between the client and the mold maker in the conventional design stage. Click the image to find out more…
Table of content
Tip: Not all mold manufacturers know about presenting the DFM report prior to mold production, and their DFM report may represent different levels of professionalism and talent. On that account, it is a nice way to evaluate the capability of the mold manufacturer.
However, it takes time and effort to have the DFM report made, so it is not a free service. Most mold manufacturers will need to receive the purchase order and the deposit payment before starting on the DFM.
Design for manufacturing (DFM) Report
Basically, the DFM will include the following information:
Here are some examples of each item:
Gate type and locations
Remark:
- In this example, the gate is located close to the corner so as to minimize part bend.
- Use the banana gates so the gate scars are at the bottom surface, there will be no visible gate scars when the part is assembled.
An example of options for injection gate design:
Remark:
- Option 1—the direct gate (or sprue gate): This is the easiest design, but there is a big scar at the center, it will be even visible from the other side (gate blush), so it is not recommended.
- Option 2—the side gate (or edge gate). This design is ok but less recommended since there will be a small gate scar at the edge, which can be visible after assembly.
- Option 3—The banana gate. The gate scar can be hidden after assembly, so this is recommended. Just that there may be some difficulty to break the gate and eject the part.
- With both options 2 and 3, it is better to have 2 cavities in the mold so the sprue can be at the center of the mold. When there is only one cavity, a hot runner may be needed.
Ejector pins type and locations
Remark:
- Since the ribs, and bosses (any feature with vertical walls) will create eject resistance, the eject pins will be designed close to these features to balance the resistance. This will avoid surface distortion (keeping them flat).
- The more ribs the part has, the ejector pins need to be designed to balance the rib resistance force.
- Ejector tubes (similar to ejector pins but hollow inside) will be placed on the bosses with holes.
Location of the parting line
Example 1
Remark:
For this plastic part, the parting line is on the largest opening and it is flat, so it is quite obvious and straightforward.
Example 2
Remark:
For this part, the design of the parting line becomes a bit tricky. Option 1 is the usual solution (where the parting line is at one end surface) for the tube-shaped plastic parts, but since this part is a bit long ( the mold needs to be very tall), which also requires the OD to have minimum or no draft angle (with a draft angle, one end will be noticeably larger than the other end), it is better to place it horizontally in the mold, so option 2 is a better choice.
In order to avoid the tube to become oval and bend, the gates are designed at the end surface. The downside of option 2 is it has a long runner, which will cause a waste of material, and result in cold slug. Anyway, we can adopt the hot runner design in order to compensate for this, .
Location of lifters and sliders
Remark:
The sliders and lifters will create parting lines, so it is helpful to indicate their locations to know if it is acceptable.
Anyway, the parting line on the outside surface will be made slight and less noticeable.
Wall and rib thicknesses analysis
Remark:
It will indicate the wall thickness with colors and mark the areas that are prone to have sink marks.
Draft angles analysis
Remark:
The draft angles are indicated by colors. The minimum draft angle depends on its texture (roughness).
Possible optimization for the part design
These optimization pieces of advice are all based on the analysis results shown above, this includes removing unnecessary undercuts, adjusting the wall thicknesses and draft angles, and so forth.
Mold Flow Analysis (MFA)
Tip: Mold flow analysis can be included in the DFM report, however, to be more concise, the mold flow analysis can be a separate section. Anyway, not all DFM reports contain mold flow analysis.
A mold flow analysis can be done for the more demanding plastic parts required to meet tight tolerances and appealing aesthetics. This mold fill simulation can predict the temperature and pressure of a production cycle, and evaluate the tendency of molding flaws.
A mold flow analysis will include the following information:
General part information (the part weight and size, the material to be used with a specific grade).
Recommended processing (molding parameters, like pressure, temperature, etc.)
Fill time (this will include an animation of the filling process).
Filling contour (it looks like a geographical contour map).
Pressure at V/P switchover (meaning switching from volume control to pressure control).
Pressure at the end of fill.
Flow Front temperature.
Bulk temperature at end of fill.
Clamp Force (this will suggest the tonnage of the injection machine to be used).
Air Traps (Tendency of air bubbles).
Weld Lines.
Volumetric shrinkage at ejection.
Sink index (the tendency of sink marks).
Temperature part at the end of cooling.
Deflection (the tendency of warpage, bend, and distortion).
Conclusions and suggestions.
The below contents are important that may have an impact on the quality of the final products, so you need to pay more attention when reading the MFA report.
Air Traps
This part has a low tendency for air traps, which means it should be good for production.
MFA is helpful in testing whether the part design and the gate location are appropriate for avoiding air traps.
Air trapping can be lessened or avoided by adjusting the injection speed.
Weld lines
This part has a medium level of tendency of having weld lines.
- Areas farther away from the injection gate are more prone to have weld lines because the temperature and pressure are lower.
- Try to avoid the weld lines to appear on the thin-walled areas, otherwise, it may cause distortion and crack in future uses.
- The visual impact of weld lines has to do with the product color and surface texture.
Note: weld lines can be made less noticeable by increasing the mold temperature, deliberately adjusting the injection speed, and so forth. However, they can not be completely eliminated.
Sink index
From the example shown in the picture, we will see the estimated amount of sinking is ≤0.0218mm, this means the wall and rib thicknesses are properly designed, and the sink marks are within the acceptable level.
Recommended criteria for different finishes:
- Textured surface: ≤0.10mm
- Painted surface: ≤0.05mm
- Plated surface: ≤0.03mm
Note: The estimated sinkings indicated by MFA are not accurate. The amount of sinking can be reduced by adjusting the injection pressure/temperature, the packing pressure/time, etc.).
Deflection
Please pay more attention to the picture Deflection in the Z direction, as it suggests, this part tends to bend on the 2 ends.
The actual amount of bend can be made less if we optimize the molding parameters by adjusting the injection pressure/temperature, the packing pressure/time, etc.
Mold drawing
Please note that the DFM does not intend to explain the details of the mold in depth, but rather to present the most important information in a concise manner. This will allow you to focus on the main issues and, at the same time, save time in producing the report.
If you want to have full details of the mold, then you should ask for the mold drawing.
The mold drawing is also very useful in case the mold needs to be repaired in the future. It has all the dimensional data that will be used for CNC machining of the mold component.
