Product Design – Stirring while microwaving

As part of my product design module I was part of a four person team where we were given the task of taking information from a customer who had an engineering problem and come up with a solution to their problem, build a prototype and test it to see if our solution solved their problem to their requirements.

Introduction to problem

The customer noticed that when he heat liquid or tried to boil water in a microwave the instructions always told him to:

  1. run the microwave  for a period of time
  2. mix the liquid
  3. run it again

When you try to stir water it can overflow the vessel it is being held in.

This is because while the heat is formed by the movement and interaction of the water molecules the liquid itself is not moving in the container due to convection and when it is stirred the sudden distribution of heat raises its temperature and it immediately boils.

The idea is for a unit that sits in the microwave and actively stirs the liquid while the microwave is operating.

This would stop water from boiling over and help prevent users from having to stir liquids like soup half way through the heating process.

Product design specifications

Product performance

The product will stir liquid at a velocity of 0.0347 metres per second. This would be due to the rotational velocity of the microwaves turning plate. It will be used for the maximum of five minutes as most microwavable food does not surpass this time frame.

If breakfast, lunch and dinner are factored in with the likely of snaking in the evening and midnight this product would be used at most five times a day. The product would not rely much on accuracy than it would on endurance and the product would harness the kinetic force of the turning plate so would not need an external energy source to power it.


  • The unit must be safe and capable of withstanding high temperatures
  • Must be capable of being submerged in a fluid
  • The main are is supported by a stabilisation leg to support the unit from shock loads.
  • The unit is made of poly-ethylene which is capable of withstanding exposure to sunlight
  • The unit is designed with a retractable spoon to allow easy access and exit of the bowl into the microwave. This will help prevent accidents from occurring when using the device.


‘Whatever works’ is a potential competitor, they sell a similar spoon for $19.99 (HouseHold, 2010)


A company called QVC Prepology Microwave Food Warmer with Auto Stir Technology is going for $9.92 (QVC, 2013)

There is also a patent for a microwave stirring member rotated by air current from the blower member for stirring microwave from the microwaves generator. (Ohnishi, 1989)

Target product cost

The target price per unit will be €14.99 and a special offer of 2 units for €25 will be available for a limited promotion time.


Primarily the product is being produced for the European market so the shipping will be within the European union postage and packaging will apply for all internet purchases.


The unit will be contained in packaging that is shaped like a small microwave.

Product life span

The product life span will be 12 months.  The material s used will be 100% recyclable

Standards and specifications

There is no quality management system in place for this product which means at this stage it does not conform to any British standards or international standard organisation standards.

The Product has not been verified that it complies with all relevant essential requirements (such as safety, health, environmental protection requirements) to gain the CE mark. However The CE marking is mandatory for certain product groups in the European Economic Area (EEA), this consist of the 27 Member States of the EU and EFTA countries Norway, Liechtenstein and Iceland.


The product has an extendable upper and lower leg, this allows for an intuitive adjustment by the user to suit different bowls. The suction cup is located at the top of the product and no adjustment of the product can be made in the x and y direction which means for the product to work the customer must stick spoon to the celling of the microwave.

Quality and reliability

No quality management system has been put in place for this product. It is believed that ISO-9000 would be persuade in order for this product to meet ISO standards and all for effective quality and reliability


Please refer to the engineering drawing contained in the appendix.


The overall unit weight will 22 grams. The reason for this is to ensure that the suction cup which holds the unit to the roof of the microwave is capable of withstanding the gross weight of the stirring unit.


The initial production of 10000 units will be produced. This initial production will be marketed in the house-ware market in the EU it will also be available for purchase on the company website and


The constrains of the current manufacturing setup in the lack of modern and efficient production unit. Many of the units currently being used are hand operated. If newer and more modern automated machines were used the production would increase dramatically.


The processes involved with this product will involve injection moulding and hand assembly of the parts.


Time scales

The product time scales will be 12 months for light use and 6 months for medium to heavy use depending on the extent of use.




The product will be tested  in a range of environments and at a range of temperatures to try and estimate the constraints and safe operating procedure of the product. A safety factor will also be applied to the device so that it is operated well within its safety zone.


According to the EU General Product Safety Directive (2001/95/EC) items must be fit-for purpose and meet any assertions which are made, such as the common claim that a product is microwave safe. Increasingly, however, users are assuming that if an item is not labeled as unsuitable for use in microwave ovens then it will automatically be safe. In 2007, EN 15284:2007 – ‘Materials and articles in contact with food stuffs – Test method for the resistance to microwave heating of ceramic, glass, glass-ceramic or plastic cookware’ was published. The intention of the standard was to provide minimum standards for all microwavable cookware. The standard includes requirements for the maximum permissible temperature and assessment of visual damage, including cracking, crazing, colour change, melting and deformation. Also covered is electrical arcing, that can occur on items with metallic decorations, and which may damage the microwave oven itself. (, 2009)

Market constraints

The constraints identified at the moment in the market are

The product is priced for upper class but would be highly needed for the working to middle class

The product would be considered as a seasonal gift or gimmick only purchased at Christmas time or as a last minute impulse by for someone as a birthday gift, mothers/ father’s day present.


  1. The product would be removed from packaging.
  2. Washed under a tap of warm (but not boiling) water.
  3. Placed in the microwave by means of the suction cup.
  4. The bowl of liquid would be placed in after the product with the adjustable leg being used to allow the spoon be placed in the bowl.


Documentation would be created with the following:

  1. operating instructions
  2. Health hazards and warnings (if any)
  3. Company contact details and customer service
  4. Product warranty
  5. How to dispose of the product

These would be translated into several languages to be used around Europe


The product would be made from polyethylene which is a thermoplastic. This means the product at its end of life could be placed in a recycling bin to be melted and reused.

Design Concepts

The following are the concepts that we came up with.

The first concept involved an uneven base surface on a bowl. The initial idea was that as the fluid moved within the bowl this would cause the bowl to oscillate on the un-even surface which in turn would cause agitation to the fluid within. However after some investigation we realised that the fluid level would remain constant and the bowl may move around the fluid meaning that there would be no agitation. See fig 1

Concept No: 1

Concept No: 1

The second concept was a mechanism which moved up and down as the microwave rotated. The idea of the movement in the upward and downward motion was to cause disruption to the flow of the material which in turn would cause agitation within the fluid. The problem with this mechanism was that it would involve a series of gears and shafts to manufacture the product. This lead to the initial idea becoming overly complex and outside the parameters of the design brief as the product was to be cheap and easy to manufacture. See fig 2.

Figure 2 Concept No: 2

Figure 2 Concept No: 2

The third concept was a device which was attached to the roof of the microwave via a suction cup. The main arm was a combination of two pieces which gave the ability for retracting the spoon when placing or removing the bowl from the microwave. The spoon is shaped like an air vent louver this allowed the fluid to change direction when it came in contact with the spoon through the louvers. This in turn causes laminar flow with in the bowl hence agitating the fluid.

Concept Selection:

The concept which we selected was the third option as it best suited our design brief. It was a simple design which was cheap to produce. We carried our initial testing on the spoon in a solid works simulation to ensure that the fluid would be diverted by the louvers to cause agitation within the bowl. The idea of the spoons ability to retract to a smaller size when entering and exiting the bowl was a factor when deciding which concept to use.

Initial Sketching:

3d modelling:


FEA analysis:

Flow analysis on Spoon

Flow analysis on Spoon

Technical Drawings:

Finished Prototype

Finished prototype

The legs were created using a laser cutter. The files had to be converted to dwf and imported to Catalyst where the part’s lines were cleaned up. After this the laser was calibrated for the chosen material and the parts cut out. We chose to cut out the parts close to the edge so that we would not use up a lot of the material.

The spoon was created in a rapid prototyper by again converting drawings into dwf format but this time it was imported into a program called rhino.

The suction cup was hot glued on and fins bent to hold the lower leg in place.


The flow simulation from the FEA proves that our initial idea was viable and met the design brief. When we tested the prototype it was successfully able to withstand the conditions met by the microwave and stirred liquid in a cup.



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