I solved it the different way. 

Instead of passing the default values from my custom module to account.invoice.
I created new button in my custom module called Create Insurance Bill.
In this method I created new invoice object and passed all header and lines info. Job beautifully done.

Here is the code..

@api.multi
    def create_insurance_bill(self):
        result = self.env['account.invoice'].create({
            'partner_id': self.insurance_partner_id.id,
            'shipment_id': self.id,
            'name': 'Insurance Bill',
            'type': 'in_invoice',
            'origin': self.name,
            'journal_id': self.insurance_journal_id.id,
            'invoice_line_ids': [(0, 0, {
                'name': self.insurance_product_id.name,
                'origin': self.name,
                'account_id': self.insurance_product_id.property_account_expense_id.id,
                'price_unit': self.insurance_amount,
                'quantity': 1.0,
                'discount': 0.0,
                'uom_id': self.insurance_product_id.uom_id.id,
                'product_id': self.insurance_product_id.id,
            })],
        })