The Renaissance Engineer: Mannequin Head Clamp Invention Job

I found a client who was in the beautician industry and had been working for many years trying to get an innovative idea to market. They had progressed to win a utility patent and conceptually know what they wished for the item to do, but needed the engineering for the mechanism to be done as well as the actual manufacturing knowledge to do the mass production details work well as well. I am in a position where I like to blend both fields of technical manufacturing and design to produce innovative solutions and here I am documenting the journey below:

In beauty school, students use mannequin heads which attach via a friction fit stud

which has a ball joint which can be clamped into position with a thread collet type mechanism.

The issue with the current product is that the heads slide off with the friction fit as you could expect such a large mass being manipulated quickly by artists at work creating their master pieces.

The invention is for a peg to spring out from the shaft to grab on to the head via a structural force instead of a friction force.

The idea is to be able to push a button and retract these pegs whenever you wish to release the mannequin head, and the button release passively allows the pegs to slide radially outwards to provide a stronger clamping force.

The items needed to accomplish this is a universal adapter that can attach to the existing inner hole liner in the neck of the mannequin.

The first adapter I thought about was a simple inner groove concept, and 3D modeled something quickly and pushed that into my 3D printing que on my Form 2 in rigid resin

However, the inner groove would still allow the mannequin head to turn in a circular groove as well as not allow such a deep detent groove to be injection molding since this undercut would be a "bump" feature which would be forced out of the injection mold and be prone to problems.

So I started thinking more about the injection molding of this adapter piece which has the tricky feature of having undercut features

This was my next idea which has alternating depth parting lined to create a undercut feature

However, this design will only work it there are pegs spaced apart at 120 degrees to work well which complicates the internal mechanism feature.

The clamping mechanism would have to be at 180 degrees due to the space constraints:

To accomodate this concept I came up with a 3 parts injection mold part of the adapter

The rounded design didn't quite fit in easily into the grooves of the existing mannequin head however:

So I went back to trying to use the original design of the peg which was a 16 sided shape to maximize the internal space

To do proper injection molded protocol in using uniform thickness to avoid weakness in improper mold

The tricky part was finding a way to design the undercuts to still fall under the concept of a sliding inner core 3 part injection mold

I printed out the concept and liked how I gave myself some breathing room to design the attachment stud

However there was a big issue that resulted from the hands on testing of the adapter. The idea was to permanently attach the adapter to the underside of the mannequin head with a strong adhesive. The issue is, the adhesive would leak into the undercut holes as well. Therefore the outside of the adapter can't have openings into the inner cavity to allow only the outside surface of the adapter, and the inside surface of the mannequin head receiver to be coated with the epoxy glue.

This really posed quite a challenge.....which I was more than eager to tackle. The solution was that the injection mold had to be more complex and perform sliding undercuts to create these detents but it had to remain in the vertical sliding core of the mold instead of the bi halve A and B mold plates

This was my first thought of using rounded peg detents that pivot in and out through an arch pin slot retraction type mechanism that as it slides down, pinches the pegs radially inward.

The "Peg" is actually the weakest link as when this breaks the entire invention is rendered useless. Therefore, it didn't make sense to create many small pegs and it was mathematically better to create at least 2 large beefy pegs in the limited space to provide the highest level of downward clamping force

The rounded peg provides some clamping force, but to get the most strength from the least amount of consumed space in this instance, it was best to have as much material in the direction of the pulling force which was in the direction of the axis of symmetry.

Any lateral loads would be taken up by the retaining shaft against the inner walls of the adapter and the only force left was the pulled force vertically that should be the main priority.

Think of how floors in a house are built, they have wide thin pieces of lumber resting on it's thinnest edge but providing the best moment of inertia for bending strength.

The ideal retaining pegs would be I-Beam shaped, but because of the conical restrictions, it was best to lop the top off and make an upside down T shape

At first I assumed the core would slide from the bottom to the top making a uniform thickness mold but then I remembered that this would be attached to a ball joint on the bottom and the critical strength would travel from the bulk of the ball joint to the end, so it was best to strengthen in in that manner

So I went forward with this design state of mind and developed the details:

The idea was to be able to push a button inward and it slides an internal member with a slanted mating face downward.

But this is where you have to think about your consumer. Most of the these users have beautiful long nails and take great pride in keeping them that way. Having to find the button and slide it inside probably catching on plastic flashing burrs probably wasn't the best feature.

So I started rethinking the button retraction mechanism that drives the conical separator part down against the spring.

A trigger that pivots on the bottom would be easier to actuate and would probably provide more torque and better pull down force from leverage. Not to mention it would be a more natural rolling and pulling force from the user to make it work.

Now for converting these sketches to CAD for further on screen brainstorming and troubleshooting:

This is a 2 part mold with one side creates undercut features to allow the button to be inserted form one end and be retained from falling out the opposite end.

The button pivots on the bottom rounded undercut and stops at the top rounded undercut

The cone geometry had to be more stubbier rather than pointy to provide enough side sliding stroke to pass through the opening in the shaft (blue) and anchor into the undercut in the adapter (Gray)

I started developing more the bottom half of the cone separator (purple) and thought it would be a good idea to hold the spring in a cavity in the middle. which can help secure it in place during assembly.

Then focused my efforts on this pivoting button design. The small neck where the cylindrical mating face meets the sliding linear surface isn't the most efficient.

So I opted to redesign the cone separator (purple) to make it symmetrical to make assembly easier both because there isn't a wrong way to insert the piece, and before you had to wedge it from the left to center and up which is a complicated movement.

Now the button has a more beefy geometry where the thinnest member is the tip of the cylindrical head which can wear away instead of snap. and the cone separator (purple) can be assembled by placing it through the top opening of the shaft (blue)

To secure everything and give the thin upper walls of the shaft some structure stability a "shaft core" was developed to provide strength and alignment of the sliding mechanisms.

The sliding members have to have some sort of retaining spring to keep them in constant contact with the mating surface of the cone.

So I thought about adding an O-ring at it's center of mass as a cost effective and strong solution. I also cross slotted that groove in the same direction as the conical mating face to provide a better retaining structure on the o - ring to prevent slippage over time.

There was one issue with this which was the shaft core has these live hinge detents which snap and secure it in place and the o ring would essentially pull the clips inward making the core slip out possibly.