The Gate smart lock is an all-in-one solution for home access. It provides door entry with or without a key, and when paired to a smartphone via the app, the camera and microphone on the lock helps the homeowner see and talk with anyone who comes to the door. This also allows for remote access for a range of purposes such as receiving deliveries.
The lock was designed by Gate Labs, a group of entrepreneurs dedicated to providing solutions for busy people who increasingly manage their lives via e-commerce, smartphone and computer.
It took three months of design iterations before the first prototype was made. From that initial prototype, more than 10 different designs were tried and tested before arriving at the current version.
A complex product such as this needs to not only function perfectly but it must also satisfy a number of aesthetic challenges. Does it look and feel like something that is high quality? Is it secure and robust? Will it blend in with different homes, apartments and office designs? One of the reasons that Gate chose to work with Star Rapid is that the team was convinced the company could provide a sophisticated fit and finish while still keeping the development costs down.
Design for manufacturing review
Achieving a great finished result required getting all the details right before the first cut was made. To do this, Star Rapid completed a design for manufacturing (DFM) review to check that the design was optimised for manufacturing and to address any potential problem areas. As part of the DFM review, the firm's engineers looked over Gate Lab’s 2D and 3D CAD files for the eight separate components.
In some areas Star Rapid suggested a change to the design or a replacement material. In other areas it was necessary to confirm with the client any process parameters that would affect the finished part, such as the location of gate marks and parting lines for injection moulding tools. Through the DFM review the following feedback was provided for discussion with the client:
Pressure die casting
Lock tab. To achieve a tighter tolerance while also reducing cost, Star Rapid recommended using zinc instead of aluminium. Zinc is more dense but has a lower melting point, which makes it easier to die cast.
Front enclosure. The narrow slots are for the speaker. In the original design these were too thin and too close together for the company to pressure die cast.
Speaker grill. To solve this the experts recommended increasing the wall thickness to a minimum of 1mm and adding a draft angle. The parting line of the mould tool was then located in between grooves to disguise it, which was later machined smooth.
Battery. The client asked for an area to be polished, but the two teams compromised on sandblasting as quicker and less expensive. This part was later nickel-plated for corrosion protection and to make a clean, uniform appearance.
Plastic injection moulding
Plastic cover. The gate mark, which is where molten plastic enters the cavity of the mould tool, was sanded off, which helped the cover snap firmly into place.
Post-machining
After pressure die casting, several areas on the shell and internal components needed post-machining to achieve the final specifications. A few areas requiring special attention were identified.
Rear base plate. Part of this area is a sliding contact so it was machined flat after die casting for a smooth rotation.
Front base plate. It’s impossible to create threads via pressure die casting alone, so Star Rapid drilled and threaded all holes to the correct dimensions.
Front enclosure. A circular opening was chamfered and smoothed out to make a precise hole for the camera lens.
Rear shell. Some areas were initially designed with draft angles for the pressure die casting process. Later the team machined them at right angles, allowing for a tighter fit of the entire assembly.
Making the mould tools
Six mould tools for eight components were made: one for compression moulding of the membrane rubber keypads; one for plastic injection moulding of the plastic cover, and four pressure die casting tools. Note that one complete mould tool consists of a separate cavity side and core side.
Tool One – compression moulding
Compression moulding tools. The male and female halves were CNC machined out of #50 carbon spring steel. Several different Shore hardnesses of EPDM rubber were tried, between Shore 30 up to Shore 90, so the client could test which one has the best reception from the market.
Tool Two – plastic injection moulding
EDM Machining. Star Rapid machined the pocket from a standard blank. This blank is a modular unit designed to fit the company's Master Unit Die, which lets any mould tool fit into any of its plastic injection moulding machines regardless of the part design or size.
Filing. Careful hand-fitting and filing lets the mould insert slide into and out of the cavity smoothly. This is a hand-loaded insert, but for larger volumes this would be automated.
Tool Three – pressure die casting
The rear shell and battery were pressure die cast in aluminium alloy using a single mould tool. Note that liquid metal enters the tool from the bottom, near the sprue. It travels through the runner, fills the cavity, and then excess material is pushed out of the overflows.
Tool Four – pressure die casting
Front and rear base plate tooling, core side. These two parts were cast in zinc from a single mould.
Tool Five – pressure die casting
Front enclosure cavity and core. The sprue is a cone-shaped protrusion, which is where the molten metal enters the tool. The sprue will also create a handle that is convenient for removing the part from the tool after injection.
How it was made – pressure die casting
The core side of the front enclosure mould tool, mounted inside the pressure die casting machine.
Ejector pins push the finished part off of the core. This is why draft angles are so important, since without them the part would stick too tightly to the core and could not be removed without damaging it.
A releasing agent such as mineral oil is sprayed onto the tool between cycles, to help the next part slide off more easily.
Excess metal is pushed out of the overflows. The team breaks off these tabs and recycles them.
Belt sanding is used to sand down the rough edge of the die casting after the excess metal is removed.
