There are two possible way of drafting.
-Drafting as a sketch and
-Drafting as a feature
Which is most suitable one for molding? Because I found sketch drafting is the easiest one for molding.
Both working fine, it depends of the complexity or some situations of your products...on plastic is usual 1° but you could need a upper value on some part of your product and at this case you could need to use draft face.
I would argue there are more than two options.
Regardless, they both have their place depending on what form you are attempting to model. Tooling designers don't care how you applied the draft, as long as it was done correctly.
and at some cases...you need to use negative draft.....damn designers....LoL
Maha, we typically draft from the "sketch" using the Boss/Cut Extrude but I would have to agree with the other comments that it's dependent on your end goal.
What I would add is that IMHO it comes down to the manufacturing process that will be used to fabricate the product.
The majority of our product and the tooling that creates our castings are conventionally machined. Being that this is the case it requires taper on the radii due to the tooling (draft mill) that will be used to create the feature. This essentially gives us a variable radius fillet.
Occasionally, we will have a customer that requires a constant radius fillet on the edge of their product. When this situation occurs we will typically have to put a different plan in place and use a Wire EDM or other manufacturing method to create this type of fillet as we cannot conventionally machine it without the use of a 5-Axis CNC. It can be done on a drafted surface but all the surfacing required to generate that type of feature simply takes too much time for us and we prefer to go the Wire EDM route.
Nothing like reverse engineering a customers import model to recreate it the correct way!
Newell, we do this all the time. More often than not the customer fully understands that we need draft on the product to assist in de-molding or removing the casting from the mold. What they never seem to get is the difference in radii from one style to another. It's always been a battle, one that we typically concede to the customer.
Over the years we have done our best to put design guidelines in place for any customer that wants to supply us with their own geometry. This can be hit or miss to say the least. Translation from one country to another is a big part of the problem. In the end it's irrelevant because the customer is always right, even when they're clearly not.
On automotive part....negative draft has usually used on it. At this case...CUMSA can help you....
1-5N2K8J6 wrote: There are two possible way of drafting. -Drafting as a sketch and-Drafting as a feature Which is most suitable one for molding? Because I found sketch drafting is the easiest one for molding.
For the most part, any method of creating draft is perfectly acceptable for molding. As a general rule, the design (not the designer...the design) dictates which drafting methods can be used, and there is almost always more than one way to do something and still get the desired end result.
Maha wrote: -Drafting as a sketch and-Drafting as a feature
I am trying to picture "drafting as a sketch". I guess in a Revolved Base feature, you can sketch the draft and get it all the way around. Yes, if it's a revolved feature, I am more likely to put the draft in the sketch. For a linear extrude, though, sketched draft won't yield draft at the ends of the extrude. I still might do that, if it served a purpose, but more likely not.
I'd say the main two ways of adding draft are the . . .
If the design allows, I'll use the Draft feature, late in the process, to keep things simple at the start, but often the draft is integral to some details and needs to come in early.
Oh I am aware, I did tool design for 2+ years. I am not sure I agree with your statement that you cannot machine a constant radius without a 5-axis though.. could you expand on that? I routinely made drafted pockets and then added radii in after the fact to intentionally keep them true to simplify the milling on 3-axis CNC machines.
When designing a part for molding (not for the real world) on and off I go and do draft analysis to see whether it has clearly defined + and - draft for molding (I mean no yellow faces). How do you do in the real world?
1-5N2K8J6 wrote: When designing a part for molding (not for the real world) on and off I go and do draft analysis to see whether it has clearly defined + and - draft for molding (I mean no yellow faces). How do you do in the real world?
Could you please try to clearly explain just what you mean by "How do you do in the real world?"
Are you asking how we check draft? Or how we create draft?
I do both but mostly on feature
I frequently check for draft analysis from the beginning when I design a part for molding therefore draft analysis will be perfect when I come to the point of checking, no drafting is needed when doing draft analysis. If you are modeling a part for manufacturing purpose (real world) how do you do? Checking from beginning or not.
imho,..however you want to pre/post draft in your part design, always do Draft Analysis, never assume.
You design for the method of manufacture. If you can visualize inverse tool geometry and proper tooling splits & shutoffs theres no reason you can't start drafting immediately in the design process. If it is added in later, that is fine also. There is no "real world" vs "not real world" design approaches. Think more in line of additive vs subtractive manufacturing technologies and their respective limitations. The finished part is either drafted correctly or it isn't. How you got there is arbitrary.
Drafting is the thing you do at the end of a part design
You'd concern more about part's functions than drafting; however, keep in mind during the design process if your part is mouldable, but not to add draft for each feature you add to your part but leave it to the end as well as chamfers and fillets - here is a folder structures of a plastic part
Newell Voss wrote: You design for the method of manufacture. If you can visualize inverse tool geometry and proper tooling splits & shutoffs theres no reason you can't start drafting immediately in the design process. If it is added in later, that is fine also. There is no "real world" vs "not real world" design approaches. Think more in line of additive vs subtractive manufacturing technologies and their respective limitations. The finished part is either drafted correctly or it isn't. How you got there is arbitrary.
Newell Voss wrote:
Wait a minute ...
You asked question about part to be molded or tooling to mold the part ?
I believe he is referring to the part modeling process in preparation for molding. The model will dictate the tooling geometry.
Drafting as a feature
Wjhat you mean here?
you mean add draft angle in the feature such as extruded Boss/Cut feature or use draft feature to add draft?
"It's complicated" is probably the best summary of my answer. I am most likely to add draft features to my part near the end of the feature tree (after most of the geometry before the rounds). Occasionally, I will include the draft as part of the extrude feature, but only on simpler parts. (Having surfaces that are not drafted, usually gives me more options to use faces for sketch planes that are going the direction I want.) I spend a fair amount of time thinking about how to do the draft to work well with my design. BUT, sometimes, the draft is important to the industrial design of the part. In that case, it is likely that the major parts of the draft are early in the model.
I try to do draft analysis pretty regularly as I am working on a model and also before I send it out for molding.I have also found, that it isn't uncommon when we get ready to mold the part for the molder to want to adjust the parting line location and the direction of draft on some surfaces. This is especially true for shutoff areas. I make my first pass at the draft angles then discuss with molder and change where I can an negotiate on the other surfaces.
Newell ... In the most basic sense possible to represent the topic at hand ...
Constant Radii: (I have no idea how to do this in a 3-Axis CNC, Not saying it can't be done, just saying I have never done something like this, ever ... Honestly, I can't even picture making a four sided pocket with taper on a CNC or Bridgeport without a sign table and a whole heck of a lot of skill. Even then I would imagine the corners would be simply miserable to get done properly)
Variable Radii: (This is what radii are produced using a draft mill on a CNC, Milling Machine or similar)
Don't agree as it can be done with profile cut around the perimeter (4 corners)
It is accomplished with a series of roughing and constant z finishing passes typically using a ball mill on an automated station.
here is an example of surface contouring on a 3 axis:
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